[ASan] Put several function prototypes back under #ifdef _WIN32 to fix the Windows build.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@175743 91177308-0d34-0410-b5e6-96231b3b80d8
[ASan] Revert the incorrect macro on Linux.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@175745 91177308-0d34-0410-b5e6-96231b3b80d8
[ASan] Declare CreateThread as extern "C" to fix the Windows build.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@175760 91177308-0d34-0410-b5e6-96231b3b80d8