Preserve external CMAKE_C_FLAGS and CMAKE_CXX_FLAGS definitions.
Preserve external CMAKE_C_FLAGS and CMAKE_CXX_FLAGS definitions.

mpflanzer/Oclgrind,mpflanzer/Oclgrind,surround-io/oclgrind,bitfusionio/Oclgrind,mpflanzer/Oclgrind,surround-io/oclgrind,bitfusionio/Oclgrind,bitfusionio/Oclgrind,surround-io/oclgrind,bitfusionio/Oclgrind,mpflanzer/Oclgrind,surround-io/oclgrind