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/cpptools.pro

@@ -107,7 +107,8 @@ equals(TEST, 1) {
         cpplocatorfilter_test.cpp \
         symbolsearcher_test.cpp \
         cpppreprocessor_test.cpp \
-        cpppreprocessertesthelper.cpp
+        cpppreprocessertesthelper.cpp \
+        cppheadersource_test.cpp
 
     HEADERS += \
         cpppreprocessertesthelper.h \