[flang] Add dependency on libSemantics to libEvaluate.

When building flang with LLVM HEAD, the unittests fail to link with ld.bfd or
ld.gold due to a linker ordering issue. Adding libSemantics as a dependency to
libEvaluate seems to fix that issue.

Reviewed at: https://github.com/flang-compiler/f18/pull/1104