<sys/cdefs.h>: Add some macros needed for our <tgmath.h>.

Taken-from: FreeBSD
gcc: Stop installing GCC's tgmath.h to /usr/libdata/gcc{44,47}.

Before this commit, the recently imported <tgmath.h> (in
/usr/include when installed) wasn't taken because of GCC's
own copies in /usr/libdata/gcc{44,47}, which comes first
in the compiler's internal include search path.

Since it is a standard header, we want our version to be
taken, so stop installing GCC's version and remove it via
'make upgrade'.

There are no other standard headers in /usr/libdata/gcc{44,47}.
gcc44: Bring back an accidentally removed file.
<sys/cdefs.h>: Bring in a compatibility macro for C11's _Static_assert.

Apparently gcc47 has support outside of C11, but for processing our
<complex.h> with gcc44, this is necessary.

Taken-from: FreeBSD