[Driver] Default LoongArch to -fno-direct-access-external-data for non-PIC (#72221)

For -fno-pic, if an extern variable is defined in a DSO, a copy
relocation will be needed. However, loongarch*-linux does not and will
not support copy relocations.

Change Driver to default to -fno-direct-access-external-data for
LoongArch && non-PIC.
Keep Frontend conditions unchanged (-fdirect-access-external-data ||
-fno-direct-access-external-data && PIC>0 => direct access).

Fix #71645