Clang: Add diagnostics

Diagnostics are now moved to the clang backend process. Fixits are
supported too.

Change-Id: I20faacf466bbf78dec479220c3d7b336a47bc453
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>

src/plugins/clangcodemodel/clangcodemodel.pro

@@ -29,6 +29,7 @@ SOURCES += \
     clangmodelmanagersupport.cpp \
     clangprojectsettings.cpp \
     clangprojectsettingspropertiespage.cpp \
+    clangtextmark.cpp \
     clangutils.cpp \
     completionchunkstotextconverter.cpp \
     cppcreatemarkers.cpp \
@@ -67,6 +68,7 @@ HEADERS += \
     clangmodelmanagersupport.h \
     clangprojectsettings.h \
     clangprojectsettingspropertiespage.h \
+    clangtextmark.h \
     clangutils.h \
     completionchunkstotextconverter.h \
     constants.h \