Lets the macro-assembler compile RISC-V C-Extension instructions
when the corresponding flag is set during runtime.

Change-Id: I443d026653b9945ac7ccff41b0ca3f7db9b65775
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3039384Reviewed-by: Brice Dobry <brice.dobry@futurewei.com>
Reviewed-by: Ji Qiu <qiuji@iscas.ac.cn>
Commit-Queue: Ji Qiu <qiuji@iscas.ac.cn>
Cr-Commit-Position: refs/heads/master@{#76128}