Fix macos bug deleting too many files

Since ruby#10209 we've been noticing that on macos after running `make
clean` the `coroutine/arm64/Context.S` file is missing, causing
subsequent make calls to fail because `Context.S` is needed to build
`Context.o`.

The reason this is happening is because macos is case-insensitive so the
`.s` looks for `coroutine/arm64/Context.s` and finds
`coroutine/arm64/Context.s`. This does not happen on linux because the
filesystem is case sensitive.

I attempted to use `find` because it is case sensitive regardless of
filesystem, but it was a lot slower than `rm` since we can't pass
multiple file names the same way to `find`.

Reverting this small part of ruby#10209 fixes the issue for macos and it
wasn't clear that those changes were strictly necessary for the rest of
the PR.

We changed the original code to use `rm` instead of `delete` because it
is not standarized on POSIX.

template/Makefile.in

@@ -493,9 +493,8 @@ clean-local::
 	  enc/encinit.c enc/encinit.$(OBJEXT) $(pkgconfig_DATA) \
 	  ruby-runner.$(OBJEXT) ruby-runner.h \
 	|| $(NULLCMD)
-	@$(RM) $(ALLOBJS:.$(OBJEXT)=.bc)
-	@$(RM) $(ALLOBJS:.$(OBJEXT)=.i)
-	@$(RM) $(ALLOBJS:.$(OBJEXT)=.s)
+	$(Q)find . ! -type d \( -name '*.bc' -o -name '*.[is]' \) -exec rm -f {} + || true
+
 
 distclean-local::
 	$(Q)$(RM) \