build: tweak macros for Windows build

Move the windows specific macro definitions for compiling c++ into the
target.  Add a number of newer options that are necessary to properly
build libc++ for windows.  This ensures that we do not accidentally
autolink msvcprt (Microsoft's C++ runtime library), do not define linker
pragmas which are msvcprt specific, and do not accidentally encode the
incorrect version of the msvc compatibility version.

llvm-svn: 290837