Don't look up DOCTYPE when resolving SDK settings on Mac OS

We don't want to hit the network, as a flakey network or slow server will
hang the XML parsing. We assume the XML is well formed.

Change-Id: Idc4898a925a46222954bf633a04ea9fe148c6797
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>

mkspecs/features/mac/sdk.prf

@@ -24,6 +24,7 @@
 
     # We use xml as the output format instead of json since plutil on 10.6 does not have that option
     QMAKE_MAC_PLATFORM_NAME = $$system("plutil -convert xml1 \"$$QMAKE_MAC_SDK_PATH/SDKSettings.plist\" -o - | " \
+        "sed '/^<!DOCTYPE/d' | " \ # Don't look up http://www.apple.com/DTDs/PropertyList-1.0.dtd
         "PERL5LIB= xpath 'string(//key[.=\"PLATFORM_NAME\"]/following-sibling::*[1])' 2>&1 | " \
         "sed 's/.*Value: \\(.*\\)/\\1/'")