RFR: JDK-8249195: Change to Xcode 11.3.1 for building on Macos at Oracle

[Erik Joelsson]

Please review this change which changes the compiler version used to 
build for Macos at Oracle to Xcode 11.3.1.

Bug: https://bugs.openjdk.java.net/browse/JDK-8249195

Webrev: http://cr.openjdk.java.net/~erikj/8249195/webrev.01/index.html

/Erik