Hi,

Currently try_compile is specified as..

try_compile (${VARIABLE}
        "${CMAKE_BINARY_DIR}" "${_check_file}"
        COMPILE_DEFINITIONS "${CMAKE_REQUIRED_DEFINITIONS}" -DGFLAGS_NAMESPACE=${_namespace}
        LINK_LIBRARIES "${gflags_LIBRARIES}"
        CMAKE_FLAGS -DINCLUDE_DIRECTORIES:STRING="${gflags_INCLUDE_DIR}"
        OUTPUT_VARIABLE OUTPUT)

However, when ${CMAKE_BINARY_DIR} is set to /home/amitprakash/CLionProjects/or-tools/cmake-build-manual/glog_project/src/glog and ${gflags_INCLUDE_DIR} is set to /home/amitprakash/CLionProjects/or-tools/cmake-build-manual/gflags_project/src/gflags/include, the build command generated by try_compile is ..

/usr/bin/c++ -DGFLAGS_NAMESPACE=google -I/home/amitprakash/CLionProjects/or-tools/cmake-build-manual/glog_project/src/glog/CMakeFiles/CMakeTmp/\"/home/amitprakash/CLionProjects/or-tools/cmake-build-manual/gflags_project/src/gflags/include\" -fPIE -o CMakeFiles/cmTC_6795b.dir/DetermineGflagsNamespace.cxx.o -c /home/amitprakash/CLionProjects/or-tools/cmake-build-manual/glog_project/src/glog/CMakeFiles/CMakeTmp/DetermineGflagsNamespace.cxx

I'm unsure why, but the include dir has changed from an ABSPATH to a RELPATH of the form ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/${gflags_INCLUDE_DIR}

The same happens when glog is installed to /usr/include, but the try_compile succeeds anyways, since /usr/include is part of system include dirs