[CMake] CMAKE_PUSH_CHECK_STATE()

[Micha Renner]

Hallo,

CMAKE_PUSH_CHECK_STATE() CMAKE_POP_CHECK_STATE() affect 
CMAKE_REQUIRED_FLAGS, CMAKE_REQUIRED_DEFINITIONS,
CMAKE_REQUIRED_LIBRARIES and CMAKE_REQUIRED_INCLUDES.

Maybe one can extend CMAKE_PUSH_CHECK_STATE() CMAKE_POP_CHECK_STATE() to
controll CMAKE_EXTRA_INCLUDE_FILES also.

Michael Renner