According to the spec, Zce is an alias for Zca, Zcb, Zcmp, and Zcmt.
If F is enabled on RV32 it also includes Zcf.
This patch adds the Zce and the implication rule which unfortunately
requires custom handling for adding Zcf.
I've also made all the Zc* extensions imply Zca.
I've also added an error for Zcf without RV32.
Reviewed By: asb
Differential Revision: https://reviews.llvm.org/D153742
0aecddcee9