Merge pull request #261 from TallFurryMan/bugfix__gentoo_gcc_fortify_…

…source

Avoid using _FORTIFY_SOURCE on systems where compiler predefines it.

libindi/CMakeLists.txt

@@ -9,6 +9,7 @@ set(CMAKE_INCLUDE_CURRENT_DIR ON)
 
 include(GNUInstallDirs)
 include(FeatureSummary)
+include(CheckCCompilerFlag)
 
 if(ANDROID OR "${CMAKE_SYSTEM_NAME}" STREQUAL "Android")
   set(ANDROID ON)
@@ -34,7 +35,16 @@ ENDIF ()
 
 # Add security (hardening flags)
 IF (UNIX OR APPLE OR ANDROID)
-    SET(SEC_COMP_FLAGS "-D_FORTIFY_SOURCE=2 -fstack-protector-all -fPIE")
+    # Older compilers are predefining _FORTIFY_SOURCE, so defining it causes a
+    # warning, which is then considered an error. Second issue is that for
+    # these compilers, _FORTIFY_SOURCE must be used while optimizing, else
+    # causes a warning, which also results in an error. And finally, CMake is
+    # not using optimization when testing for libraries, hence breaking the build.
+    CHECK_C_COMPILER_FLAG("-Werror -D_FORTIFY_SOURCE=2" COMPATIBLE_FORTIFY_SOURCE)
+    IF (${COMPATIBLE_FORTIFY_SOURCE})
+        SET(SEC_COMP_FLAGS "-D_FORTIFY_SOURCE=2")
+    ENDIF ()
+    SET(SEC_COMP_FLAGS "${SEC_COMP_FLAGS} -fstack-protector-all -fPIE")
     # Make sure to add optimization flag. Some systems require this for _FORTIFY_SOURCE.
     IF (NOT CMAKE_BUILD_TYPE MATCHES "MinSizeRel" AND NOT CMAKE_BUILD_TYPE MATCHES "Release" AND NOT CMAKE_BUILD_TYPE MATCHES "Debug")
         SET(SEC_COMP_FLAGS "${SEC_COMP_FLAGS} -O1")