cl/gcc: include required headers when compiling against gcc-4.9.x
cl/gcc: use gimple_code(), gimple_bb(), and gimple_location()

... instead of accessing struct members directly
cl/gcc: compile with -fno-rtti if C++ linkage is used

Otherwise the resulting GCC plug-in fails to link due to missing symbol
_ZTI8opt_pass (typeinfo for opt_pass).
cl/gcc: use C++ style passes plugging with gcc-4.9.0
cl/storage: get isDefined() ready for g++ built-ins