RFR: 8268719: Force execution (and source) code page used when compiling on Windows

[Saint Wesonga]

Set MSVC source and execution character sets to UTF-8 to enable Visual C++ to compile all source files regardless of the active code page on Windows. This avoids build errors due to "warning C4819: The file contains a character that cannot be represented in the current code page (932). Save the file in Unicode format to prevent data loss"

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Commit messages:
 - Set MSVC source and execution character sets to UTF-8

Changes: https://git.openjdk.org/jdk/pull/15569/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15569&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8268719
  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/15569.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15569/head:pull/15569

PR: https://git.openjdk.org/jdk/pull/15569