Update feature paths on assignment to QMAKE_PLATFORM

Instead of after parsing the makespecs, were we assumed QMAKE_PLATFORM
had been set by the makespec and did an explicit update.

Allows loading platform specific features from within a makespec after
updating QMAKE_PLATFORM.

Change-Id: I0eb3b7fb88ce48b00a384850c5d87223c06234d7
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>
(cherry picked from qtbase/4dd29248cd43ff730f7432b51a443b72fad3523d)

src/shared/proparser/qmakeevaluator.cpp

@@ -114,6 +114,7 @@ void QMakeEvaluator::initStatics()
     statics.strforever = QLatin1String("forever");
     statics.strhost_build = QLatin1String("host_build");
     statics.strTEMPLATE = ProKey("TEMPLATE");
+    statics.strQMAKE_PLATFORM = ProKey("QMAKE_PLATFORM");
 #ifdef PROEVALUATOR_FULL
     statics.strREQUIRES = ProKey("REQUIRES");
 #endif
@@ -912,6 +913,8 @@ void QMakeEvaluator::visitProVariable(
 
     if (varName == statics.strTEMPLATE)
         setTemplate();
+    else if (varName == statics.strQMAKE_PLATFORM)
+        updateFeaturePaths();
 #ifdef PROEVALUATOR_FULL
     else if (varName == statics.strREQUIRES)
         checkRequirements(values(varName));
@@ -1202,7 +1205,6 @@ bool QMakeEvaluator::loadSpec()
     }
     if (!loadSpecInternal())
         return false;
-    updateFeaturePaths(); // The spec extends the feature search path, so rebuild the cache.
     if (!m_conffile.isEmpty()
         && !evaluateFile(m_conffile, QMakeHandler::EvalConfigFile, LoadProOnly)) {
         return false;

src/shared/proparser/qmakeevaluator_p.h

@@ -77,6 +77,7 @@ struct QMakeStatics {
     QString strforever;
     QString strhost_build;
     ProKey strTEMPLATE;
+    ProKey strQMAKE_PLATFORM;
 #ifdef PROEVALUATOR_FULL
     ProKey strREQUIRES;
 #endif