GL: suppress a Clang warning in the test.

src/Magnum/GL/Test/AbstractShaderProgramGLTest.cpp

@@ -1284,6 +1284,11 @@ void AbstractShaderProgramGLTest::compute() {
 /* These are outside of any namespace to verify the macros fully qualify all
    names */
 namespace {
+    /* Yes, Clang, I know, the macros add unused members. That's fine. */
+    #ifdef CORRADE_TARGET_CLANG
+    #pragma GCC diagnostic push
+    #pragma GCC diagnostic ignored "-Wunused-member-function"
+    #endif
     struct ShaderSubclassDraw: Magnum::GL::AbstractShaderProgram {
         MAGNUM_GL_ABSTRACTSHADERPROGRAM_SUBCLASS_DRAW_IMPLEMENTATION(ShaderSubclassDraw)
     };
@@ -1292,6 +1297,9 @@ namespace {
         MAGNUM_GL_ABSTRACTSHADERPROGRAM_SUBCLASS_DISPATCH_IMPLEMENTATION(ShaderSubclassDispatch)
     };
     #endif
+    #ifdef CORRADE_TARGET_CLANG
+    #pragma GCC diagnostic pop
+    #endif
 }
 
 namespace Magnum { namespace GL { namespace Test { namespace {