RFR: 8304930: Enable Link Time Optimization as an option for Visual C++

[Julian Waters]

Currently, Link Time Optimization is only available for Java Virtual Machines compiled with gcc. Since the Java VM is the most performance critical part of the Java Platform for obvious reasons, it follows that optimized executables produced for Windows (as Visual C++ is currently the only compiler available for Windows as [JDK-8288293](https://bugs.openjdk.org/browse/JDK-8288293) is still under heavy development) would grant a significant performance boost for Java on Windows as a whole. Flags used for link time optimizations are set to make compiling with it enabled as fast as possible, to avoid the pitfall of very long compile times

Depends on [JDK-8304893](https://bugs.openjdk.org/browse/JDK-8304893) being integrated first, to prove that link time optimization is viable as an option

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Commit messages:
 - Add to task list
 - Create new job for link time optimized builds
 - Missing ifeq
 - Merge branch 'openjdk:master' into patch-7
 - 8304930: Enable Link Time Optimization as an option for Visual C++

Changes: https://git.openjdk.org/jdk/pull/13280/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13280&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304930
  Stats: 19 lines in 2 files changed: 18 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13280.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13280/head:pull/13280

PR: https://git.openjdk.org/jdk/pull/13280