Support specifying explicit SDK version

https://bugs.webkit.org/show_bug.cgi?id=274298

Reviewed by Elliott Williams.

Strip the version number from the specified SDK as well when setting
the platform name

* Tools/Scripts/webkitdirs.pm:
(determineXcodeSDKPlatformName):

Canonical link: https://commits.webkit.org/279009@main

Tools/Scripts/webkitdirs.pm

@@ -965,7 +965,7 @@ sub determineXcodeSDKPlatformName {
     if (checkForArgumentAndRemoveFromARGVGettingValue("--sdk", \$sdk)) {
         $xcodeSDK = lc $sdk;
         $xcodeSDKPlatformName ||= $sdk;
-        $xcodeSDKPlatformName =~ s/\.internal$//;
+        $xcodeSDKPlatformName =~ s/(\d+\.[\d\.]+)?(\.internal)?$//;
         die "Couldn't determine platform name from Xcode SDK" unless isValidXcodeSDKPlatformName($xcodeSDKPlatformName);
         return;
     }