[flang] Function 'attributeTypeIsCompatible' should be debug only (NFC)

/data/home/jiefu/llvm-project/flang/lib/Optimizer/CodeGen/CodeGen.cpp:2905:20: error: unused function 'attributeTypeIsCompatible' [-Werror,-Wunused-function]
static inline bool attributeTypeIsCompatible(mlir::MLIRContext *ctx,
                   ^
1 error generated.