LoongArch: Check PC-relative relocations for shared libraries

Building shared libraries should not be allowed for PC-relative
relocations against external symbols.
Currently LoongArch has no corresponding checks and silently
generates wrong shared libraries.

However, In the first version of the medium cmodel, pcalau12i+jirl was
used for function calls, in which case PC-relative relocations were
allowed.
11 files changed