[LLD][ELF] Add FORCE_LLD_DIAGNOSTICS_CRASH to force LLD to crash

Add FORCE_LLD_DIAGNOSTICS_CRASH inspired by the existing
FORCE_CLANG_DIAGNOSTICS_CRASH.

This is particularly useful for people customizing LLD as they may
want to modify the crash reporting behavior.

Differential Revision: https://reviews.llvm.org/D128195