Include QMAKE_CC when extracting C compiler flags

This fixes cross-compile settings detection for cross-compilation
environments where the C compiler cross-compilation flags are set in
CC/QMAKE_CC instead of CFLAGS/QMAKE_CFLAGS (e.g. OpenEmbedded).

Change-Id: I0a7b0f6c47a00775ec18073a16359c8351363285
Reviewed-by: Andras Becsi <andras.becsi@digia.com>

tools/qmake/mkspecs/features/functions.prf

@@ -35,7 +35,7 @@ defineReplace(getChromiumSrcDir) {
 }
 
 defineReplace(extractCFlag) {
-    CFLAGS = $$QMAKE_CFLAGS
+    CFLAGS = $$QMAKE_CC $$QMAKE_CFLAGS
     !isEmpty(ANDROID_TARGET_CFLAGS): CFLAGS = $$ANDROID_TARGET_CFLAGS
     OPTION = $$find(CFLAGS, $$1)
     OPTION = $$split(OPTION, =)