Various things:
* work around -Wnullability-completeness.
* use C++ casts in C++ and C casts in C.
* stop using attributes clang doesn't support (such as `warning`).
* remove duplicate definitions of XATTR_CREATE and XATTR_REPLACE.
Change-Id: I07649e46275b28a23ca477deea119fe843999533
Found by passing a bad regular expression to the Google benchmark
code (https://github.com/google/benchmark).
Change-Id: I475db71c25706bbf02091b754acabe8254062f3a
<signal.h> shouldn't get you the contents of <errno.h>, and <fcntl.h>
shouldn't get you the contents of <unistd.h>.
Change-Id: I347499cd8671bfee98e6b8e875a97cab3a3655d3
GCC assembler allows xyz to be redeclared as weak,
by __weak_alias(xyz, _xyz), while _xyz is undefined.
Clang does not like that but silently generates no code.
It will reject its own .s file if the assembly code is saved first.
Since we have no reason to define xyz or _xyz as weak symbol now,
and _xyz is a macro to xyz, we simplify libC to have only
xyz defined as global.
BUG: 17186746
Change-Id: I24b154425838683cae69248cc750c59e26fd5467
