base/asm-common.h, *.S: Include metadata for 64-bit Windows stack unwinding.

There are (annoyingly undocumented) assembler directives, which make
this fairly straightforward.  I've manually verified that they're
setting up the expected data structures correctly.  Under normal
circumstances, we don't expect these leaf functions to throw exceptions.

Note that the `endswap_block' subroutine of `rijndael_setup_x86ish_-
aesni' is not currently properly described.