Fix MIPS waitid build.

Fix MIPS waitid build.

As previously discussed in
<https://sourceware.org/ml/libc-alpha/2012-11/msg00798.html>, MIPS (o32)
waitid has build warnings (now errors) because a function is declared
inline but functions with five-argument syscalls cannot be inlined for
MIPS o32.

This patch disables the -Winline warnings for waitid.c using a
MIPS-specific wrapper file.  As it's whole-file disabling, there's no
point in using push and pop, so just DIAG_IGNORE_NEEDS_COMMENT is
used.

	* sysdeps/unix/sysv/linux/mips/mips32/waitid.c: New file.