[OpenMP] Enable position independent code for libomptarget

Summary:
This option used to be passed manually by the `-fPIC` option that was
always enabled by the LLVM flags. Since we now do this manually we want
to specify that these are supposed for use fPIC code.
GitOrigin-RevId: 71e3082d8572fd335dcc994fd63a75d69b9d2b2e
2 files changed