[jfx11u] Integrated: 8270479: WebKit 612.1 build fails with Visual Studio 2017

[Kevin Rushforth]

Clean backport of the fix to allow WebKit to continue to build with VS 2017, as a follow-on to the WebKit 612.1 update, so it is based off that branch. Once PR #34 is integrated, I will rebase this branch on top of `master` (to pick up that fix), and take this out of Draft state.

As an FYI, I tested this patch in my [test-kcr-11.0.13](https://github.com/kevinrushforth/jfx11u/tree/test-kcr-11.0.13) branch, which has the aggregate set of patches for the following bugs: [JDK-8211308](https://bugs.openjdk.java.net/browse/JDK-8211308), [JDK-8268915](https://bugs.openjdk.java.net/browse/JDK-8268915), [JDK-8269147](https://bugs.openjdk.java.net/browse/JDK-8269147), [JDK-8269131](https://bugs.openjdk.java.net/browse/JDK-8269131), [JDK-8268849](https://bugs.openjdk.java.net/browse/JDK-8268849), [JDK-8270479](https://bugs.openjdk.java.net/browse/JDK-8270479), [JDK-8272329](https://bugs.openjdk.java.net/browse/JDK-8272329).

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Commit messages:
 - 8270479: WebKit 612.1 build fails with Visual Studio 2017

Changes: https://git.openjdk.java.net/jfx11u/pull/35/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx11u&pr=35&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8270479
  Stats: 21 lines in 3 files changed: 21 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx11u/pull/35.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx11u pull/35/head:pull/35

PR: https://git.openjdk.java.net/jfx11u/pull/35