remove redundant feature test macro checks in sys/time.h

this header is XSI-shaded itself and thus does not need to limit
specific content to _XOPEN_SOURCE.

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.

add nonstandard timespec/timeval conversion macros in sys/time.h

these are poorly designed (illogical argument order) and even poorly
implemented (brace issues) on glibc, but unfortunately some software
is using them. we could consider removing them again in the future at
some point if they're documented as deprecated, but for now the
simplest thing to do is just to provide them under _GNU_SOURCE.

timeradd/timersub: cast result to void to get rid of warnings

previously:
timersub(&now, t, &diff);

warning: value computed is not used [-Wunused-value]

fix the prototype of settimeofday to follow the original BSD declaration

add obsolete futimesat()

this function is obsolete, however it's available as a syscall
and as such qemu userspace emulation tries to forward it to the
host kernel.

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.

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 legacy futimes and lutimes functions

based on patch by sh4rm4. these functions are deprecated; futimens and
utimensat should be used instead in new programs.

fix and cleanup suseconds_t/timeval stuff (broken on 64-bit)

trash in the upper 32 bits was making the kernel sleep forever in
select on 64-bit systems.

add legacy BSD-style timer*() macros in sys/time.h

cleanup namespace in sys/time.h

extensive header cleanup for standards conformance & correctness

thanks to Peter Mazinger (psm) for pointing many of these issues out
and submitting a patch on which this commit is loosely based

initial check-in, version 0.5.0