Minor build system fix.

* Move perform_feature_checks() before GCC configuration to allow compiler
  option tests to be recognized during the first build when no cache file
  exists.

CMakeLists.txt

@@ -115,6 +115,11 @@ if( NOT DEFAULT_INSTALL_PATH )
          "Location of KiCad data files." )
 endif()
 
+# Generate build system specific header file.
+include( PerformFeatureChecks )
+perform_feature_checks()
+
+
 #================================================
 # Set flags for GCC, or treat llvm as GCC
 #================================================
@@ -563,10 +568,6 @@ endif()
 # Include MinGW resource compiler.
 include( MinGWResourceCompiler )
 
-# Generate build system specific header file.
-include( PerformFeatureChecks )
-perform_feature_checks()
-
 # Find GDI+ on windows if wxGraphicsContext is available.
 if( MINGW AND USE_WX_GRAPHICS_CONTEXT )
     find_package( GdiPlus )