As discussed in following pr's, the flag `RestoreMXCSROnJNICalls` is used on several platforms, x86, aarch64, and riscv (coming), but the name is x86ish, so it's better to give it a generic name, and it's better to do it in a seperate pr rather than in https://github.com/openjdk/jdk/pull/18839 which is a riscv specific pr, and this task definitely needs a csr I guess?

https://github.com/openjdk/jdk/pull/16851#issuecomment-1838915879, https://github.com/openjdk/jdk/pull/18839#issuecomment-2066150874