[External][SPEC2000] Add -Wl,-zmultidef linker option.

The SPEC CPU 2000 benchmarks 186.crafty and 300.twolf have symbols
defined in multiple source file. Add the -zmultidef option to the
linker for compatibility with older linkers.

Reviewed By: naromero77

Differential Revision: https://reviews.llvm.org/D95276