ProjectExplorer: Filter out non-applicable toolchains

... when filling the "parent toolchain" combo box for clang on Windows.
We should not offer the user a mingw C compiler as the parent of a clang
C++ compiler. Even though it will probably work (as it's mainly there
for the sysroot), it's conceptually weird and it blows up the number of
entries for no good reason.

Change-Id: Ic920993b4ff36f8d8d095392555dc9d27f376878
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/projectexplorer/gcctoolchain.cpp

@@ -1720,8 +1720,11 @@ void ClangToolChainConfigWidget::updateParentToolChainComboBox()
         return;
 
     for (const ToolChain *mingwTC : mingwToolChains()) {
-        if (parentId != mingwTC->id())
-            m_parentToolchainCombo->addItem(mingwTC->displayName(), mingwTC->id());
+        if (mingwTC->id() == parentId)
+            continue;
+        if (mingwTC->language() != tc->language())
+            continue;
+        m_parentToolchainCombo->addItem(mingwTC->displayName(), mingwTC->id());
     }
 }