[clang] [clang][LoongArch] Don't imply -fdirect-access-external-data for non-PIC (PR #71887)

[Fangrui Song via cfe-commits]

MaskRay wrote:

Thanks for the patch, but I think we can keep the default only in the default so that Frontend does not need to handle target-specific differences. See 
https://github.com/llvm/llvm-project/pull/72221 and I've added only few tests that make sense (`-fpic -fdirect-access-external-data` generally doesn't make sense. Newer tests should use `--target=`. We should also avoid relying on the -fno-pic default for baremetal.)

https://github.com/llvm/llvm-project/pull/71887