When using --with-macosx-sdk=10.8 or 9, use xcode-select -print-path

I want to be able to use of a separate Xcode installation (like a
developer preview) instead of the /Applications/Xcode.app one.

Change-Id: I1faa84d028a8df6b4fc61b321fd2a6cde9a0ab0f

configure.ac

@@ -2701,13 +2701,9 @@ if test $_os = Darwin; then
             fi
             ;;
         10.8|10.9)
-            if test -d "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX$with_macosx_sdk.sdk"; then
-                MACOSX_SDK_PATH=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX$with_macosx_sdk.sdk
-            else
-                xcodepath="`xcode-select -print-path`"
-                if test -d "$xcodepath/Platforms/MacOSX.platform/Developer/SDKs/MacOSX$with_macosx_sdk.sdk"; then
-                    MACOSX_SDK_PATH="$xcodepath/Platforms/MacOSX.platform/Developer/SDKs/MacOSX$with_macosx_sdk.sdk"
-                fi
+            xcodepath="`xcode-select -print-path`"
+            if test -d "$xcodepath/Platforms/MacOSX.platform/Developer/SDKs/MacOSX$with_macosx_sdk.sdk"; then
+                MACOSX_SDK_PATH="$xcodepath/Platforms/MacOSX.platform/Developer/SDKs/MacOSX$with_macosx_sdk.sdk"
             fi
             ;;
         esac