Clang: Introduce CompilerMacro

We want not only the name but the value of the macro too. So we can
compare if anything has changed.

Change-Id: Ie59caf8cbf54d108f9e15299d25306a406b5c40d
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

tests/unit/unittest/refactoringclientserverinprocess-test.cpp

@@ -178,7 +178,7 @@ TEST_F(RefactoringClientServerInProcess, SendUpdatePchProjectPartsMessage)
 {
     ProjectPartContainer projectPart2{"projectPartId",
                                       {"-x", "c++-header", "-Wno-pragma-once-outside-header"},
-                                      {"DEFINE"},
+                                      {{"DEFINE", "1"}},
                                       {{1, 1}},
                                       {{1, 2}}};
     FileContainer fileContainer{{"/path/to/", "file"}, "content", {}};