Add no-pic debug flag to disable position independent code

Probably don't want to be adding to the number of debug flags, but there seemed to be interest in adding this in #10942.

From the LLVM source DynamicNoPIC is "Relocatable external references, non-relocatable code". On platforms it isn't supported on it becomes either RelocStatic or RelocPIC.

Again, I haven't written a test. I couldn't see any existing ones for PIC stuff. Passes existing tests though.