cc: experimental -fast option for tcc/codegen in the future

vlib/compiler/cc.v

@@ -64,6 +64,7 @@ fn (v mut V) cc() {
 	// TCC on Linux by default, unless -cc was provided
 	// TODO if -cc = cc, TCC is still used, default compiler should be
 	// used instead.
+	if v.pref.fast {
 		$if linux {
 		$if !android {
 			vdir := os.dir(vexe)
@@ -85,6 +86,9 @@ fn (v mut V) cc() {
 				v.pref.ccompiler = tcc_path
 			}
 		}
+		} $else {
+			verror('-fast is only supported on Linux right now')
+		}	
 	}
 	//linux_host := os.user_os() == 'linux'
 	v.log('cc() isprod=$v.pref.is_prod outname=$v.out_name')

vlib/compiler/main.v

@@ -114,6 +114,7 @@ pub mut:
 						 // work on the builtin module itself.
 	//generating_vh bool
 	comptime_define string  // -D vfmt for `if $vfmt {`
+	fast bool // use tcc/x64 codegen
 }
 
 // Should be called by main at the end of the compilation process, to cleanup
@@ -930,6 +931,7 @@ pub fn new_v(args[]string) &V {
 		is_run: 'run' in args
 		autofree: '-autofree' in args
 		compress: '-compress' in args
+		fast: '-fast' in args
 		is_repl: is_repl
 		build_mode: build_mode
 		cflags: cflags