moc: force the Microsoft compiler not to define _MSC_EXTENSIONS

This re-fixes commit d72ac3f35f, which
simply removed the #define but did so at the wrong place. Instead of
forcing the macro to be removed, let's simply not have it defined in the
first place.

Change-Id: Ie6dbad9bbbd9488887e8fffd148dd67d9a31b32e
Reviewed-by: Jake Petroules <jake.petroules@qt.io>

mkspecs/features/moc.prf

@@ -31,10 +31,10 @@ if(gcc|intel_icl|msvc):!rim_qcc:!uikit {
     moc_predefs.name = "Generate moc_predefs.h"
     moc_predefs.CONFIG = no_link
     gcc:            moc_predefs.commands = $$QMAKE_CXX $$QMAKE_CXXFLAGS -dM -E -o ${QMAKE_FILE_OUT} ${QMAKE_FILE_IN}
-    else:intel_icl: moc_predefs.commands = $$QMAKE_CXX $$QMAKE_CXXFLAGS -QdM -P -Fi${QMAKE_FILE_OUT} ${QMAKE_FILE_IN}
+    else:intel_icl: moc_predefs.commands = $$QMAKE_CXX $$QMAKE_CXXFLAGS -QdM -P -Za -Fi${QMAKE_FILE_OUT} ${QMAKE_FILE_IN}
     else:msvc {
         moc_predefs.commands += $$QMAKE_CXX -Bx$$shell_quote($$shell_path($$QMAKE_QMAKE)) $$QMAKE_CXXFLAGS \
-                                    -E ${QMAKE_FILE_IN} 2>NUL >${QMAKE_FILE_OUT}
+                                    -E -Za ${QMAKE_FILE_IN} 2>NUL >${QMAKE_FILE_OUT}
     } else:         error("Oops, I messed up")
     moc_predefs.output = $$MOC_DIR/moc_predefs.h
     moc_predefs.input = MOC_PREDEF_FILE

src/tools/moc/main.cpp

@@ -477,9 +477,6 @@ int runMoc(int argc, char **argv)
     }
     moc.symbols += pp.preprocessed(moc.filename, &in);
 
-    // We obviously do not support MS extensions
-    pp.macros.remove("_MSC_EXTENSIONS");
-
     if (!pp.preprocessOnly) {
         // 2. parse
         moc.parse();