I've reported the wcsftime bug upstream, but we really just want to use -D
to ensure the buggy code isn't built. (I've also brought our strftime a bit
closer to upstream now we have the right define.)
I don't think upstream is likely to fix all their sign-compare and
uninitialized warnings, so let's just silence them.
As for libm, again upstream isn't likely to fix all their warnings, and
silencing those made the ones that were our fault stand out. I've fixed
our <math.h> to fix the warnings caused by our lack of definitions for
the non-imprecise long-double functions. I checked the C99 standard, and
all these functions are there.
Change-Id: Iee8e1182c1db375058fb2c451eceb212bab47a37
