[msan] Disable DynamoRio detection.

This code is not robust enough and triggers when simply linking with
libdynamorio.so, without any code translation at all. Disabling it is safe
(i.e. we may unpoison too much memory and see false negatives, but never false
positives).
[Sanitizers] Rename Symbolizer::SymbolizeCode to Symbolizer::SymbolizePC
ARM: update comment to match reality
[Sanitizer] Implement Symbolizer class on Windows
One ppc32-darwin, a i64 inside a structure can have 32 bit alignment.

Thanks for Iain Sandoe for testing this with the original gcc.

Clang was already getting this right.
[Sanitizers] Fix CL compile-time warning in the symbolizer