RFR: 8247283: Enable the new conformant preprocessor option in Visual Studio

[Magnus Ihse Bursie]

The new conformant preprocessor has been feature complete since Visual Studio 2019.

We should start to use it instead of the traditional preprocessor (which is well known to be non-conforming in various ways). This would bring VS-based usage more in line with other platforms in this area, and remove the need for some workarounds for the traditional preprocessor's behavior. 

This PR is dependent on [JDK-8293162](https://bugs.openjdk.org/browse/JDK-8293162) "Drop support for VS2017" and [JDK-8293088](https://bugs.openjdk.org/browse/JDK-8293088) "Fix compilation with the new Visual Studio preprocessor".

-------------

Commit messages:
 - 8247283: Enable the new conformant preprocessor option in Visual Studio

Changes: https://git.openjdk.org/jdk/pull/10101/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10101&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8247283
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/10101.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10101/head:pull/10101

PR: https://git.openjdk.org/jdk/pull/10101