[Beignet] [PATCH 5/7] Backend: Refine LLVM version check macro

[Song, Ruiling]

> -#if LLVM_VERSION_MAJOR == 3 && LLVM_VERSION_MINOR >= 9
> +#if LLVM_VERSION_MAJOR * 10 + LLVM_VERSION_MINOR >= 39

I think it is better to add "LLVM_VERSION" in llvm_includes.hpp:
#define LLVM_VERSION (LLVM_VERSION_MAJOR * 10 + LLVM_VERSION_MINOR)
So at each place we only check LLVM_VERSION against a specific version number.
Like #if LLVM_VERSION >=39

Thanks!
Ruiling