ci: fix coutput_test.v on windows by fixing `-o -` on windows

vlib/v/builder/cc.v

@@ -479,7 +479,7 @@ fn (mut v Builder) cc() {
 		}
 		return
 	}
-	if v.pref.out_name.ends_with('/-') {
+	if v.pref.should_output_to_stdout() {
 		// output to stdout
 		content := os.read_file(v.out_name_c) or { panic(err) }
 		println(content)

vlib/v/builder/compile.v

@@ -107,7 +107,7 @@ fn (mut b Builder) run_compiled_executable_and_exit() {
 	if b.pref.only_check_syntax {
 		return
 	}
-	if b.pref.out_name.ends_with('/-') {
+	if b.pref.should_output_to_stdout() {
 		return
 	}
 	if b.pref.os == .ios {

vlib/v/gen/c/coutput_test.v

@@ -12,15 +12,7 @@ const testdata_folder = os.join_path(vroot, 'vlib', 'v', 'gen', 'c', 'testdata')
 
 const diff_cmd = diff.find_working_diff_command() or { '' }
 
-fn test_windows() ? {
-	$if windows {
-		eprintln('this test can not run on windows for now')
-		exit(0)
-	}
-}
-
 fn test_out_files() ? {
-	eprintln('> vroot: $vroot')
 	println(term.colorize(term.green, '> testing whether .out files match:'))
 	os.chdir(vroot)
 	output_path := os.join_path(os.temp_dir(), 'coutput', 'out')
@@ -41,7 +33,7 @@ fn test_out_files() ? {
 		print(term.colorize(term.magenta, 'v run $relpath') + ' == ' +
 			term.colorize(term.magenta, out_relpath) + ' ')
 		pexe := os.join_path(output_path, '${basename}.exe')
-		compilation := os.execute('VCOLORS=never $vexe -o $pexe $path')
+		compilation := os.execute('$vexe -o $pexe $path')
 		ensure_compilation_succeeded(compilation)
 		res := os.execute(pexe)
 		if res.exit_code < 0 {
@@ -108,7 +100,7 @@ fn test_c_must_have_files() ? {
 		basename, path, relpath, must_have_relpath := target2paths(must_have_path, '.c.must_have')
 		print(term.colorize(term.magenta, 'v -o - $relpath') + ' matches all line paterns in ' +
 			term.colorize(term.magenta, must_have_relpath) + ' ')
-		compilation := os.execute('VCOLORS=never $vexe -o - $path')
+		compilation := os.execute('$vexe -o - $path')
 		ensure_compilation_succeeded(compilation)
 		expected_lines := os.read_lines(must_have_path) or { [] }
 		generated_c_lines := compilation.output.split_into_lines()
@@ -128,6 +120,9 @@ fn test_c_must_have_files() ? {
 		}
 		if nmatches == expected_lines.len {
 			println(term.green('OK'))
+		} else {
+			eprintln('> ALL lines:')
+			eprintln(compilation.output)
 		}
 	}
 	assert total_errors == 0
@@ -154,8 +149,10 @@ fn normalize_panic_message(message string, vroot string) string {
 	return msg
 }
 
-fn vroot_relative(path string) string {
+fn vroot_relative(opath string) string {
-	return path.replace(os.path_separator, '/').replace('$vroot/', '').replace('./', '')
+	nvroot := vroot.replace(os.path_separator, '/') + '/'
+	npath := opath.replace(os.path_separator, '/')
+	return npath.replace(nvroot, '')
 }
 
 fn ensure_compilation_succeeded(compilation os.Result) {
@@ -167,23 +164,11 @@ fn ensure_compilation_succeeded(compilation os.Result) {
 	}
 }
 
-[if etrace ?]
-fn etrace(msg string) {
-	eprintln(msg)
-}
-
 fn target2paths(target_path string, postfix string) (string, string, string, string) {
-	etrace('')
-	etrace('> target2paths $target_path | postfix: $postfix')
 	basename := os.file_name(target_path).replace(postfix, '')
-	etrace('           basename: $basename')
 	target_dir := os.dir(target_path)
-	etrace('         target_dir: $target_dir')
 	path := os.join_path(target_dir, '${basename}.vv')
-	etrace('               path: $path')
 	relpath := vroot_relative(path)
-	etrace('            relpath: $relpath')
 	target_relpath := vroot_relative(target_path)
-	etrace('     target_relpath: $target_relpath')
 	return basename, path, relpath, target_relpath
 }

vlib/v/pref/pref.v

@@ -695,6 +695,10 @@ pub fn (pref &Preferences) vrun_elog(s string) {
 	}
 }
 
+pub fn (pref &Preferences) should_output_to_stdout() bool {
+	return pref.out_name.ends_with('/-') || pref.out_name.ends_with(r'\-')
+}
+
 pub fn arch_from_string(arch_str string) ?Arch {
 	match arch_str {
 		'amd64', 'x86_64', 'x64', 'x86' { // amd64 recommended