RFR: 8251858: Update to Xcode 11.3.1

[Ambarish Rapte]

On Fri, 28 Aug 2020 18:39:16 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

> This updates the compiler used to build JavaFX on macOS to Xcode 11.3.1 + MacOSX10.15 sdk, which matches the compiler
> used to build JDK 16.
> As noted in the bug report, Xcode 11.3.1 needs macOS 10.14.4 (Mojave) or later to build, but the produced artifacts
> will be able to run on earlier versions of macOS.

Build verified on Mojave 10.14.6

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Marked as reviewed by arapte (Reviewer).

PR: https://git.openjdk.java.net/jfx/pull/291