Try to speedup tst_qmetatype.cpp compilation with clang.

The test instantiates enormous amounts of templates in one compilation
unit. All clang versions, that I tested, suffers from performance issues
while compiling the test, the cost depends on the version. The most
affected are shipped by Apple.

Task-number: QTBUG-37237

Change-Id: I0959c1a4a6faee448ae1dae5c1e70ee06cefbd9c
Reviewed-by: Simo Fält <simo.falt@digia.com>
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>

tests/auto/corelib/kernel/kernel.pro

@@ -21,10 +21,6 @@ SUBDIRS=\
     qvariant \
     qwineventnotifier
 
-# Building the qmetatype test with Clang on ARM takes forever (QTBUG-37237)
-!clang|!contains(QT_ARCH, arm): \
-    SUBDIRS += qmetatype
-
 !qtHaveModule(gui): SUBDIRS -= \
     qmimedata
 

tests/auto/corelib/kernel/qmetatype/qmetatype.pro

@@ -15,3 +15,18 @@ win32-msvc*|wince|winrt {
         QMAKE_CFLAGS_RELEASE -= -O2
     }
 }
+
+clang {
+    # clang has some performance problems with the test. Especially
+    # with automaticTemplateRegistration which creates few thousands
+    # template instantiations (QTBUG-37237). Removing -O2 and -g
+    # improves the situation, but it is not solving the problem.
+    QMAKE_CXXFLAGS_RELEASE -= -O2
+    QMAKE_CFLAGS_RELEASE -= -O2
+    QMAKE_CXXFLAGS_RELEASE -= -g
+    QMAKE_CFLAGS_RELEASE -= -g
+
+    # Building for ARM (eg iOS) is affected so much that we disable
+    #the template part of the test
+    contains(QT_ARCH, arm): DEFINES += TST_QMETATYPE_BROKEN_COMPILER
+}