QT7: Remove usage of QMAKE_MAC_XARCH

Support for QMAKE_MAC_XARCH was removed in Qt 5.0, so it shouldn't be
used in the QT7 plugin, as it causes build failures.

Task-number: QTBUG-27180
Change-Id: I7d907a9afbcbc4989b794350c94d0f619e4d2b7d
Reviewed-by: Caroline Chao <caroline.chao@digia.com>

src/plugins/qt7/qt7.pro

@@ -20,14 +20,10 @@ LIBS += -framework AppKit -framework AudioUnit \
         -framework AudioToolbox -framework CoreAudio \
         -framework QuartzCore -framework QTKit
 
-# The Quicktime framework is only awailable for 32-bit builds, so we
-# need to check for this before linking against it.
-# QMAKE_MAC_XARCH is not awailable on Tiger, but at the same time,
-# we never build for 64-bit architechtures on Tiger either:
-contains(QMAKE_MAC_XARCH, no) {
+# QUICKTIME_C_API_AVAILABLE is true only on i386
+# so make sure to link QuickTime
+contains(QMAKE_HOST.arch, i386) {
     LIBS += -framework QuickTime
-} else {
-    LIBS += -Xarch_i386 -framework QuickTime -Xarch_ppc -framework QuickTime
 }
 
 HEADERS += \