[debugger] Expose ngunwind as a public library.

I plan to use ngunwind from garnet in some debugger code.

Change-Id: Ie18fa5d94847c1c5efff63c21c9b6db27ce8b8f2

[build] Rename x86 project to "x64"

Build output will now be in build-x64 instead of build-x86
Renamed and updated various scripts as appropriate

Within zircon, $ARCH remains "x86".
This avoids having to rename kernel/arch/x86/ and change a lot of #include paths
Removed unnecessary $SUBARCH build variable

Renamed the kernel target from pc-x86 to pc, and the board name in boards.list
from "x86" to "pc".

Change-Id: I0eb44a21ba731653b92f3ce2b78a7819c0a8f61c

[ulib][ngunwind] Force -O2

This library does not build with -Og, so force -O2 on a
module level.

Change-Id: I353cb3e45126eceac9c4c99ee68f999455983f12

[third_party][ngunwind] Remove arm32 from the build.

Change-Id: I85d23b727c68b0d053ca9d93bc296a0f689d8474

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[build] flatten the build

Previously we treated kernel/, system/, and third_party/ as
overlays on a shared namespace. This required the concept
of "canonical" module names, and a lot of complexity to ensure
that things didn't collide and the build worked.

This change gets rid of that, no longer passes -I to make,
so that include directives from our *.mk files do not magically
wildcard across various paths, etc.

The most user-visible change is that everywhere where a module
name is specified (MODULE_DEPS, MODULE_LIBS, etc), full module
names like kernel/lib/io or system/ulib/mxio must be used instead
of previously-allowed "short" names like lib/io and ulib/mxio.

The build output still has a similar shape, but the first segment
of the module path (kernel/, system/, or third_party/) is no
longer elided under $(BUILDDIR)

Change-Id: I525aba1da1c86eb7a86007bddc669f7eeebfedd5

[build][musl] refer to musl libc as ulib/c

This makes the build rules and the intermediate
output files easier to understand, without having
to modify the path where musl libc lives.

The biggest observeable difference is the build
intermediate files:

$ ls build-magenta-pc-x86-64/ulib/c
config-module.h libc.abi.h libc.abi.stamp libc.so libc.so.id libc.so.strip
libc.a libc.abi.o libc.a.opts libc.so.abi libc.so.opts third_party

which previously were at build-magenta-pc-x86/ulib/musl
and named libmusl.*

and the replacing of ulib/musl with ulib/c in the library
dependencies of all the rules.mk files (the vast bulk of
this change)

Change-Id: If9c5d522099d2c9ac5bdb666b8e67a2eb3d316ee

[ulib][ngunwind][backtrace] Export for use by Fuchsia.

Change-Id: I7d2170c4152adff84aa11c409c92bcd0a7cf9097

[ngunwind] move headers to include/ngunwind

Originally in include/libunwind, which is a bit confusing
and potential conflict.

Change-Id: Ia760cbeda0614577bd4389570f322a8efea5d17c

[ulib][ngunwind] Use -Wno-absolute-value for Clang

This crufty code has some insane things in it. Rather than figuring out
the brain damage in code we don't intend to keep using for the long run,
just disable the warnings Clang gives for it.

Change-Id: Ic5f9447bc92007c789dbbd6becec3f880619d6ef

[kernel][build] Move KEEP_FRAME_POINTER to MODULE_COMPILEFLAGS.

Change-Id: I1233a10c7ee412a9ee2c18891bdb1d94ad0e461e

[ulib][ngunwind] Add rules.mk.

Change-Id: I707a10fe30b4232fa65c695b21bc18054bf3de56