Clang: Fix path to intrinsics dir

...which got lost in

    commit 1e3f2eec8d
    Clang: Consolidate all ClangCompilerOptionsBuilder into one implementation

This will fix

    SOFT ASSERT: "!resourceDir.isEmpty()" in file
        C:\work\build\qt-creator\src\plugins\cpptools\clangcompileroptionsbuilder.cpp,
        line 119

Change-Id: Ie0301517eca580b4907bbcd8f524775f2b0bedb8
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/cpptools/clangcompileroptionsbuilder.cpp

@@ -38,7 +38,7 @@ namespace CppTools {
 static QString creatorResourcePath()
 {
 #ifndef UNIT_TESTS
-    return Core::ICore::instance()->resourcePath();
+    return Core::ICore::instance()->libexecPath();
 #else
     return QString();
 #endif