[msan] Intercept fstatat / fstatat64.
test: Handle libc++ shared lib name on FreeBSD

(I didn't take a guess at the Linux names, as these tests are currently
skipped with the comment "No standard locations for libc++ on Linux.")
A better way to silence the warning in MSVC (replaces r190304).
[ARMv8] Prevent generation of deprecated IT blocks on ARMv8 in Thumb mode.
IT blocks can only be one instruction lonf, and can only contain a subset of
the 16 instructions.

Patch by Artyom Skrobov!