[CIR][NFC] Add LLVM and OGCG checks to six codegen tests (#191536)
Add CIR-to-LLVM and classic codegen RUN lines to empty.cpp,
c89-implicit-int.c, expressions.cpp, binop.c, forward-enum.c, and
static-vars.c so each test verifies LLVM IR output from both pipelines.
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