Remove stat wrapper functions, move them to exported symbols

This patch removes the stat, stat64, lstat, lstat64, fstat, fstat64,
fstatat, and fstatat64 static wrapper and add the symbol on the libc
with the expected names.

Both the prototypes of the internal symbol linked by the static
wrappers and the inline redirectors are also removed from the installed
sys/stat.h header file.  The wrapper implementation license LGPL
exception is also removed since it is no longer statically linked to
binaries.

Internally the _STAT_VER* definitions are moved to a arch-specific
xstatver.h file.  The internal defines that redirects internals
{f}stat{at} to their {f}xstat{at} counterparts are removed for Linux
(!NO_RTLD_HIDDEN).  Hurd still requires them since {f}stat{at} pulls
extra objects that makes the loader build fail otherwise (I haven't
dig into why exactly).

Checked with a build for all affected ABIs. I also checked on x86_64,
i686, powerpc, powerpc64le, sparcv9, sparc64, s390, and s390x.

Reviewed-by: Lukasz Majewski <lukma@denx.de>