Merge pull request #5003 from jbeich/clang

input_common: unbreak -Werror with Clang

src/input_common/CMakeLists.txt

@@ -56,8 +56,8 @@ else()
         -Werror=reorder
         -Werror=shadow
         -Werror=sign-compare
-        -Werror=unused-but-set-parameter
-        -Werror=unused-but-set-variable
+        $<$<CXX_COMPILER_ID:GNU>:-Werror=unused-but-set-parameter>
+        $<$<CXX_COMPILER_ID:GNU>:-Werror=unused-but-set-variable>
         -Werror=unused-variable
     )
 endif()