macx-xcode: Change wrapper to write to QMAKESPEC to change mkspec

The allows us to remove the custom logic in default_post for finding
the plist files, and also fixes issues when the wrapped mkspec had
its own feature files.

Change-Id: I4c26cf6a7809f527e170c51c57f59aaf6088774c
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>

mkspecs/macx-xcode/features/default_post.prf

@@ -1,7 +0,0 @@
-
-isEmpty(QMAKE_INFO_PLIST) {
-    plist_template = $$absolute_path(../../$$[QMAKE_XSPEC]/Info.plist.$${TEMPLATE})
-    exists($$plist_template): QMAKE_INFO_PLIST = $$plist_template
-}
-
-load(default_post)

mkspecs/macx-xcode/qmake.conf

@@ -4,6 +4,12 @@
 # OS X + Xcode
 #
 
-include(../$$[QMAKE_XSPEC]/qmake.conf)
+QMAKESPEC = $$dirname(PWD)/$$[QMAKE_XSPEC]
+
+include($$QMAKESPEC/qmake.conf)
 
 MAKEFILE_GENERATOR = XCODE
+
+# The active spec is now the original spec, but we still want
+# Xcode specific blocks to be triggered.
+CONFIG += macx-xcode