Opt-out of the build on platforms where we won't build successfully

To allow the qt5.git integration, allow the build to succeed if the
repository is checked out on a platform that we don't maintain.

This is the initial list of platforms that we want the integration
to succeed and we can add new ones once we start maintaining them.

Change-Id: Idce2a84eb8d5b1ef7f14d399fe013f666b479108
Reviewed-by: Andras Becsi <andras.becsi@digia.com>

examples/examples.pro

 TEMPLATE=subdirs
 
-SUBDIRS += webengine/quicknanobrowser
+qtHaveModule(webengine) {
+    SUBDIRS += webengine/quicknanobrowser
+}
 
 qtHaveModule(webenginewidgets) {
     SUBDIRS += \

src/src.pro

 TEMPLATE = subdirs
 
-process.depends = core
-webengine.depends = core
-webenginewidgets.depends = core webengine
-webengine_plugin.subdir = webengine/plugin
-webengine_plugin.target = sub-webengine-plugin
-webengine_plugin.depends = webengine
-webengine_experimental_plugin.subdir = webengine/plugin/experimental
-webengine_experimental_plugin.target = sub-webengine-experimental-plugin
-webengine_experimental_plugin.depends = webengine
+isPlatformSupported() {
+    process.depends = core
+    webengine.depends = core
+    webenginewidgets.depends = core webengine
+    webengine_plugin.subdir = webengine/plugin
+    webengine_plugin.target = sub-webengine-plugin
+    webengine_plugin.depends = webengine
+    webengine_experimental_plugin.subdir = webengine/plugin/experimental
+    webengine_experimental_plugin.target = sub-webengine-experimental-plugin
+    webengine_experimental_plugin.depends = webengine
 
 
-SUBDIRS += core \
-           process \
-           webengine \
-           webengine_plugin \
-           webengine_experimental_plugin
+    SUBDIRS += core \
+               process \
+               webengine \
+               webengine_plugin \
+               webengine_experimental_plugin
 
-# FIXME: We probably want a bit more control over config options to tweak what to build/ship or not.
-# Another example of where this could be necessary is to make it easy to build proprietery codecs support.
-!contains(WEBENGINE_CONFIG, no_ui_delegates): SUBDIRS += webengine/ui
+    # FIXME: We probably want a bit more control over config options to tweak what to build/ship or not.
+    # Another example of where this could be necessary is to make it easy to build proprietery codecs support.
+    !contains(WEBENGINE_CONFIG, no_ui_delegates): SUBDIRS += webengine/ui
 
-qtHaveModule(widgets) {
-    SUBDIRS += webenginewidgets
+    qtHaveModule(widgets) {
+        SUBDIRS += webenginewidgets
+    }
+} else {
+    warning("QtWebEngine is not maintained on this platform and is therefore disabled.")
 }

tests/tests.pro

 TEMPLATE = subdirs
-SUBDIRS +=  auto quicktestbrowser
 
+isPlatformSupported() {
+    SUBDIRS +=  auto quicktestbrowser
+}

tools/qmake/mkspecs/features/functions.prf

+defineTest(isPlatformSupported) {
+  linux-g++|win32-msvc2013|macx-clang: return(true)
+  return(false)
+}
+
 # Map to the correct target type for gyp
 defineReplace(toGypTargetType) {
   equals(TEMPLATE, "app"):return("executable")