fix various header namespace issues under feature-test-macro control

reported and changes suggested by Daniel Sabogal.

make brace placement in public header struct definitions consistent

placing the opening brace on the same line as the struct keyword/tag
is the style I prefer and seems to be the prevailing practice in more
recent additions.

these changes were generated by the command:

find include/ arch/*/bits -name '*.h' \
-exec sed -i '/^struct [^;{]*$/{N;s/\n/ /;}' {} +

and subsequently checked by hand to ensure that the regex did not pick
up any false positives.

refactor headers, especially alltypes.h, and improve C++ ABI compat

the arch-specific bits/alltypes.h.sh has been replaced with a generic
alltypes.h.in and minimal arch-specific bits/alltypes.h.in.

this commit is intended to have no functional changes except:
- exposing additional symbols that POSIX allows but does not require
- changing the C++ name mangling for some types
- fixing the signedness of blksize_t on powerpc (POSIX requires signed)
- fixing the limit macros for sig_atomic_t on x86_64
- making dev_t an unsigned type (ABI matching goal, and more logical)

in addition, some types that were wrongly defined with long on 32-bit
archs were changed to int, and vice versa; this change is
non-functional except for the possibility of making pointer types
mismatch, and only affects programs that were using them incorrectly,
and only at build-time, not runtime.

the following changes were made in the interest of moving
non-arch-specific types out of the alltypes system and into the
headers they're associated with, and also will tend to improve
application compatibility:
- netdb.h now includes netinet/in.h (for socklen_t and uint32_t)
- netinet/in.h now includes sys/socket.h and inttypes.h
- sys/resource.h now includes sys/time.h (for struct timeval)
- sys/wait.h now includes signal.h (for siginfo_t)
- langinfo.h now includes nl_types.h (for nl_item)

for the types in stdint.h:
- types which are of no interest to other headers were moved out of
the alltypes system.
- fast types for 8- and 64-bit are hard-coded (at least for now); only
the 16- and 32-bit ones have reason to vary by arch.

and the following types have been changed for C++ ABI purposes;
- mbstate_t now has a struct tag, __mbstate_t
- FILE's struct tag has been changed to _IO_FILE
- DIR's struct tag has been changed to __dirstream
- locale_t's struct tag has been changed to __locale_struct
- pthread_t is defined as unsigned long in C++ mode only
- fpos_t now has a struct tag, _G_fpos64_t
- fsid_t's struct tag has been changed to __fsid_t
- idtype_t has been made an enum type (also required by POSIX)
- nl_catd has been changed from long to void *
- siginfo_t's struct tag has been removed
- sigset_t's has been given a struct tag, __sigset_t
- stack_t has been given a struct tag, sigaltstack
- suseconds_t has been changed to long on 32-bit archs
- [u]intptr_t have been changed from long to int rank on 32-bit archs
- dev_t has been made unsigned

summary of tests that have been performed against these changes:
- nsz's libc-test (diff -u before and after)
- C++ ABI check symbol dump (diff -u before, after, glibc)
- grepped for __NEED, made sure types needed are still in alltypes
- built gcc 3.4.6

feature test macros: make _GNU_SOURCE enable everything

previously, a few BSD features were enabled only by _BSD_SOURCE, not
by _GNU_SOURCE. since _BSD_SOURCE is default in the absence of other
feature test macros, this made adding _GNU_SOURCE to a project not a
purely additive feature test macro; it actually caused some features
to be suppressed.

most of the changes made by this patch actually bring musl in closer
alignment with the glibc behavior for _GNU_SOURCE. the only exceptions
are the added visibility of functions like strlcpy which were BSD-only
due to being disliked/rejected by glibc maintainers. here, I feel the
consistency of having _GNU_SOURCE mean "everything", and especially
the property of it being purely additive, are more valuable than
hiding functions which glibc does not have.

default features: make musl usable without feature test macros

the old behavior of exposing nothing except plain ISO C can be
obtained by defining __STRICT_ANSI__ or using a compiler option (such
as -std=c99) that predefines it. the new default featureset is POSIX
with XSI plus _BSD_SOURCE. any explicit feature test macros will
inhibit the default.

installation docs have also been updated to reflect this change.

use restrict everywhere it's required by c99 and/or posix 2008

to deal with the fact that the public headers may be used with pre-c99
compilers, __restrict is used in place of restrict, and defined
appropriately for any supported compiler. we also avoid the form
[restrict] since older versions of gcc rejected it due to a bug in the
original c99 standard, and instead use the form *restrict.

fix dirent.h with _BSD_SOURCE

publicly expose getdents api under _BSD_SOURCE

add (currently stubbed due to stubbed strverscmp) versionsort function

based on patch by Emil Renner Berthing, with minor changes to dirent.h
for LFS64 and organization of declarations

this code should work unmodified once a real strverscmp is added, but
I've been hesitant to add it because the GNU strverscmp behavior is
harmful in a lot of cases (for instance if you have numeric filenames
in hex). at some point I plan on trying to design a variant of the
algorithm that behaves better on a mix of filename styles.

_GNU_SOURCE is supposed to imply _LARGEFILE64_SOURCE

this is ugly and stupid, but now that the *64 symbol names exist, a
lot of broken GNU software detects them in configure, then either
breaks during build due to missing off64_t definition, or attempts to
compile without function declarations/prototypes. "fixing" it here is
easier than telling everyone to add yet another feature test macro to
their builds.

support _BSD_SOURCE feature test macro

patch by Isaac Dunham. matched closely (maybe not exact) to glibc's
idea of what _BSD_SOURCE should make visible.

add support for ugly *64 functions with _LARGEFILE64_SOURCE

musl does not support legacy 32-bit-off_t whatsoever. off_t is always
64 bit, and correct programs that use off_t and the standard functions
will just work out of the box. (on glibc, they would require
-D_FILE_OFFSET_BITS=64 to work.) however, some programs instead define
_LARGEFILE64_SOURCE and use alternate versions of all the standard
types and functions with "64" appended to their names.

we do not want code to actually get linked against these functions
(it's ugly and inconsistent), so macros are used instead of prototypes
with weak aliases in the library itself. eventually the weak aliases
may be added at the library level for the sake of using code that was
originally built against glibc, but the macros will still be the
desired solution in the headers.

fix handling of d_name in struct dirent

basically there are 3 choices for how to implement this variable-size
string member:
1. C99 flexible array member: breaks using dirent.h with pre-C99 compiler.
2. old way: length-1 string: generates array bounds warnings in caller.
3. new way: length-NAME_MAX string. no problems, simplifies all code.

of course the usable part in the pointer returned by readdir might be
shorter than NAME_MAX+1 bytes, but that is allowed by the standard and
doesn't hurt anything.

d_fileno alias for d_ino in dirent

this is nonstandard but since POSIX reserved d_ prefix in dirent.h we
might as well define it unconditionally. some programs depend on it.

fix typos in dirent.h

add macros for use with d_type extension field in dirent

initial check-in, version 0.5.0