Update RunTests.gmk to use `-jvmArgsPrepend` to avoid overwriting built-in micro `jvmArgs` flags.
------------- Commit messages: - Use -jvmArgsPrepend for running microbenchmarks in RunTests.gmk Changes: https://git.openjdk.org/jdk/pull/21800/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21800&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8343345 Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod Patch: https://git.openjdk.org/jdk/pull/21800.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/21800/head:pull/21800 PR: https://git.openjdk.org/jdk/pull/21800
