Clang: Explicitly set the target triple

As for the analyzer, this makes us independent of the default triple and will
most likely reduce the maintenance - e.g. the target implies certain internal
command line arguments, we will profit from added ones.

This fixes parsing of mingw headers with the clang code model.

Change-Id: I722b981125a80fac5f62a7af40a83ecdd7bbf811
Reviewed-by: Christian Kandeler <christian.kandeler@theqtcompany.com>

src/plugins/cpptools/compileroptionsbuilder.h

@@ -45,6 +45,7 @@ public:
     void addDefine(const QByteArray &defineLine);
 
     // Add options based on project part
+    virtual void addTargetTriple();
     void addHeaderPathOptions();
     void addToolchainAndProjectDefines();
     virtual void addLanguageOption(ProjectFile::Kind fileKind);