runtime(compilers): ensure compiler! sets global options (#14336)

Previously some options were only set locally by
&l:makeprg/errorformat

This suffices for :compiler (without a trailing bang)
but falls short for :compiler! that sets &g:makeprg/errorformat as
well

Also apply kind suggestions by @dkearns and @lifepillar 

Signed-off-by: Konfekt <Konfekt@users.noreply.github.com>
Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/compiler/mcs.vim

@@ -1,8 +1,8 @@
 " Vim compiler file
-" Compiler:    Mono C# Compiler
-" Maintainer:  Jarek Sobiecki <harijari@go2.pl>
-" Last Updated By: Peter Collingbourne
-" Latest Revision: 2012 Jul 19
+" Compiler:     Mono C# Compiler
+" Maintainer:   Jarek Sobiecki <harijari@go2.pl>
+" Contributors: Peter Collingbourne and Enno Nagel
+" Last Change:  2024 Mar 29
 
 if exists("current_compiler")
   finish
@@ -12,7 +12,12 @@ let current_compiler = "mcs"
 let s:cpo_save = &cpo
 set cpo-=C
 
-setlocal errorformat=
+if exists(":CompilerSet") != 2 " Older Vim always used :setlocal
+  command -nargs=* CompilerSet setlocal <args>
+endif
+
+CompilerSet makeprg=mcs
+CompilerSet errorformat=
          \%D%.%#Project\ \"%f/%[%^/\"]%#\"%.%#,
          \%X%.%#Done\ building\ project\ \"%f/%[%^/\"]%#\"%.%#,
          \%-G%\\s%.%#,