Clang: Add Symbol Indexing

It is a first step and now a database is generated if you start QtCreator.
Some code is now shared with the PchManager which can be improved in the
future.

Change-Id: Ic267fe7960f6c455d91832859a673ce98f269aa2
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/tools/clangrefactoringbackend/source/clangrefactoringbackend-source.pri

@@ -9,7 +9,9 @@ HEADERS += \
     $$PWD/symbolscollectorinterface.h \
     $$PWD/symbolstorageinterface.h \
     $$PWD/symbolstorage.h \
-    $$PWD/storagesqlitestatementfactory.h
+    $$PWD/storagesqlitestatementfactory.h \
+    $$PWD/symbolindexing.h \
+    $$PWD/symbolindexinginterface.h
 
 !isEmpty(LIBTOOLING_LIBS) {
 SOURCES += \
@@ -55,4 +57,5 @@ SOURCES += \
     $$PWD/symbolindexer.cpp \
     $$PWD/symbolentry.cpp \
     $$PWD/sourcelocationentry.cpp \
-    $$PWD/symbolstorage.cpp
+    $$PWD/symbolstorage.cpp \
+    $$PWD/symbolindexing.cpp