Decouple caching of iOS/OSX SDK path and version in sdk.prf

Combining them could lead to intermediate builds having cached the
path, but not the version, resulting in later version checks failing.

Change-Id: Ia10f4268ce7b9e82c81627970236d68c00b80391
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@theqtcompany.com>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>

mkspecs/features/mac/sdk.prf

@@ -9,11 +9,15 @@ isEmpty(QMAKE_MAC_SDK.$${QMAKE_MAC_SDK}.path) {
     QMAKE_MAC_SDK_PATH = $$system("/usr/bin/xcodebuild -sdk $$QMAKE_MAC_SDK -version Path 2>/dev/null")
     isEmpty(QMAKE_MAC_SDK_PATH): error("Could not resolve SDK path for \'$$QMAKE_MAC_SDK\'")
     cache(QMAKE_MAC_SDK.$${QMAKE_MAC_SDK}.path, set stash, QMAKE_MAC_SDK_PATH)
+} else {
+    QMAKE_MAC_SDK_PATH = $$eval(QMAKE_MAC_SDK.$${QMAKE_MAC_SDK}.path)
+}
+
+isEmpty(QMAKE_MAC_SDK.$${QMAKE_MAC_SDK}.version) {
     QMAKE_MAC_SDK_VERSION = $$system("/usr/bin/xcodebuild -sdk $$QMAKE_MAC_SDK -version SDKVersion 2>/dev/null")
     isEmpty(QMAKE_MAC_SDK_VERSION): error("Could not resolve SDK version for \'$$QMAKE_MAC_SDK\'")
     cache(QMAKE_MAC_SDK.$${QMAKE_MAC_SDK}.version, set stash, QMAKE_MAC_SDK_VERSION)
 } else {
-    QMAKE_MAC_SDK_PATH = $$eval(QMAKE_MAC_SDK.$${QMAKE_MAC_SDK}.path)
     QMAKE_MAC_SDK_VERSION = $$eval(QMAKE_MAC_SDK.$${QMAKE_MAC_SDK}.version)
 }