build: pass XCODE_VERSION through to qt macOS cross compile conf

This should mostly be a no-op, however it would seem to make more sense
that we pass through the XCODE_VERSION we now have in depends, rather
than leaving the version set to 4.3.

depends/patches/qt/mac-qmake.conf

@@ -6,7 +6,7 @@ include(../common/gcc-base-mac.conf)
 include(../common/clang.conf)
 include(../common/clang-mac.conf)
 QMAKE_MAC_SDK_PATH=$${MAC_SDK_PATH}
-QMAKE_XCODE_VERSION=4.3
+QMAKE_XCODE_VERSION = $${XCODE_VERSION}
 QMAKE_XCODE_DEVELOPER_PATH=/Developer
 QMAKE_MACOSX_DEPLOYMENT_TARGET = $${MAC_MIN_VERSION}
 QMAKE_MAC_SDK=macosx