Disable PCH for qdrawhelper.cpp with GCC 5

Precompiled headers with GCC 5.3.1 causes internal compiler error in
qdrawhelper.cpp, so compile this specific file without PCH.

Task-number: QTBUG-54154
Change-Id: Id5d9fe99cbeca58a60734510898e4ccb9694c203
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/gui/painting/painting.pri

@@ -108,6 +108,12 @@ qtConfig(cssparser) {
         painting/qcssutil.cpp
 }
 
+# Causes internal compiler errors with at least GCC 5.3.1:
+gcc:equals(QT_GCC_MAJOR_VERSION, 5) {
+    SOURCES -= painting/qdrawhelper.cpp
+    NO_PCH_SOURCES += painting/qdrawhelper.cpp
+}
+
 SSE2_SOURCES += painting/qdrawhelper_sse2.cpp
 SSSE3_SOURCES += painting/qdrawhelper_ssse3.cpp
 SSE4_1_SOURCES += painting/qdrawhelper_sse4.cpp \