[ASan/Win] Enable demangling of global variable names
[asan] use some LIKELY/UNLIKELY
[ASan tests] Create a Posix/ directory for tests that we don't plan to run on Windows
[ASan tests] Update relative paths from POSIX-only tests to their shared libraries
Do not run GPGPU test cases without nvptx target

Tag the GPGPU codegen test cases as unsupported if the nvptx target is not
included in the current llvm build.

Contributed-by:  Yabin Hu <yabin.hwu@gmail.com>