build: don't add -fPIC on Windows
build: don't add -fPIC on Windows

`-fPIC` doesn't make much sense for Windows, since Windows DLLs aren't compiled
position independent and are instead relocated at runtime.

Patch by Shoaib Meenai!

git-svn-id: 756ef344af921d95d562d9e9f9389127a89a6314@280413 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx