Driver: warn on -fPIC/-fpic/-fPIE/-fpie on Windows

Use of these flags would result in the use of ELF-style PIE/PIC code
which is incorrect on Windows.  Windows is inherently PIC by means of
the DLL slide that occurs at load.  This also mirrors the behaviour on
GCC for MinGW.  Currently, the Windows x86_64 forces the relocation
model to PIC (Level 2).  This is unchanged for now, though we should
remove any assumptions on that and change it to a static relocation
model.

llvm-svn: 290533