[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[third_party][ulib][musl] Use real functions for "self" handle accessors

This puts the __magenta_*_self variables back where they belong, as
internal private variables in libc. The _mx_*_self accessor functions
are real functions again. To optimize uses inside libc itself, they
are defined internally as macros.

Change-Id: I4cc8a2616018b04e3743cc73ce9beacd280dea09

[musl] Remove unneeded VM lock

On Linux musl, this is used to serialize access to mmap()ed memory
related to robust mutex unwinding. We do not support this mechanism,
and so do not need the serialization. In particular, we also do not
need userspace synchronization to implement MAP_FIXED safely.

Change-Id: Iaf8cd1b5cdc5d4518fc3f1e6455578cb36da981a

[musl][magenta] Move process handle header into magenta

Change-Id: I00eb8f5ca7fbaf9297f3b1e5b391be00ce5d11e2

[musl] Make munmap only act on the given range

Previously, munmap would ignore the *len* argument and unmap
the entire mapping that contained *start*.

Change-Id: I9905cc7558d4c6047ed5eb7b69c0b5392f98b955

[vmar][musl] Update musl to use VMAR interfaces

Change-Id: Iecc93bc57634a0b1bc080b3260c703dc53fb00be

[headers] declare a slot for the process handle to live in

This change removes a dependency from the public/magenta/syscalls.h
onto third_party/ulib/musl/include/magenta/process.h where
mx_process_self() was previously declared. Instead, we declare
a slot in public/magenta/internal.h where the runtime is expected
to store the process handle and provide an inline accessor for it.

Change-Id: I04f080beca3ccef554b148aa0ff67a66ba189b33

[ulib][magenta][runtime][musl] Give system calls _mx_* names, use them in musl

The mx_* name space is not kosher for the standard C library to use
for its own purpose. A conforming standard C program can define its
own functions called mx_* and this must not break the C library.

Give all the system call entry points in the vDSO names starting
with _mx_, with the old mx_ names as aliases. Use only the _mx_
names in runtime and musl.

Change-Id: Id01b57b87c0bb91733e9492159401ff019943822

[magenta][syscalls] migrate all syscalls to the new names

If DEPCRECATE_COMPAT_SYSCALLS is defined, flag the compatibility
wrappers with the deprecated attribute.

Enable this in the Magenta build only for now.

Change-Id: I422b1294d9db2e56551eca65dede0e5d83f8b363

[ulib] [musl] Prepare code for using proc-self handle

This should cover all the uses of the process handle in ld.so/libc.
This is in preparation for launchpad passing the process handle and
the kernel requiring it in calls. But actually setting the value is
disabled for now, since there isn't one we can use yet.

Change-Id: I70fb363151726d0ac6537a4b0358edecadf3b5eb

[musl] First implementation of munmap.

This first pass does not support arbitrary unmappings, but appears to
handle the cases needed in malloc/free for musl.

Issue: MG-115
Change-Id: Ifecd0e70ef2e76c1502be870e6d43f49d8795e29

[magenta] Initial commit