regexp: fix compiling alternate patterns of different fold case literals
Fixing Equal method in regexp/syntax package fixes compilation of
some alternate patterns like "0A|0[aA]".
Fixes #59007
Change-Id: Idd519c6841167f932899b0ada347fb90a38a765e
GitHub-Last-Rev:
6f43cbca6361c0d084a12abeec65d7c659a4fe61
GitHub-Pull-Request: golang/go#66165
Reviewed-on: https://go-review.googlesource.com/c/go/+/569735
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Mark Freeman <mark@golang.org>
Auto-Submit: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>