patch 8.2.3922: cannot build with dynamic Ruby 3.1

Problem:    Cannot build with dynamic Ruby 3.1.
Solution:   Add "_EXTRA" variables for CI.  Add missing functions. (Ozaki
            Kiichi, closes #9420)
diff --git a/ci/config.mk.clang.sed b/ci/config.mk.clang.sed
index da6044d..9dc271c 100644
--- a/ci/config.mk.clang.sed
+++ b/ci/config.mk.clang.sed
@@ -1,2 +1,2 @@
 /^CFLAGS[[:blank:]]*=/s/$/ -Wno-error=missing-field-initializers/
-/^RUBY_CFLAGS[[:blank:]]*=/s/$/ -Wno-error=unknown-attributes -Wno-error=ignored-attributes/
+/^RUBY_CFLAGS_EXTRA[[:blank:]]*=/s/$/ -Wno-error=unknown-attributes -Wno-error=ignored-attributes/