C++: Custom directory list for Switch Header/Source

Some projects use separate directories for sources and headers.

An example tree:
*
|-- src
     |-- foo.cpp
|-- include
     |-- foo.h

Allow the user to specify directories for finding out-of-project related
header/source files, in addition to current directory

Task-number: QTCREATORBUG-8883
Change-Id: I57215c8f2feffcc246d0d161798290861bcfcdd4
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>

src/plugins/cpptools/cpptoolsplugin.h

@@ -60,6 +60,9 @@ public:
     ~CppToolsPlugin();
 
     static CppToolsPlugin *instance();
+    static const QStringList &headerSearchPaths();
+    static const QStringList &sourceSearchPaths();
+    static void clearHeaderSourceCache();
 
     bool initialize(const QStringList &arguments, QString *errorMessage);
     void extensionsInitialized();
@@ -211,6 +214,9 @@ private slots:
     void test_builtinsymbolsearcher();
     void test_builtinsymbolsearcher_data();
 
+    void test_headersource_data();
+    void test_headersource();
+
 private:
     void test_completion();
 #endif