tools: fix building `vdoctor.v` with `v build-tools`

cmd/tools/modules/testing/common.v

@@ -471,7 +471,7 @@ pub fn prepare_test_session(zargs string, folder string, oskipped []string, main
 		// for example module import tests, or subtests, that are compiled/run by other parent tests
 		// in specific configurations, etc.
 		if fnormalised.contains('testdata/') || fnormalised.contains('modules/')
-			|| f.contains('preludes/') {
+			|| fnormalised.contains('preludes/') {
 			continue
 		}
 		$if windows {
@@ -489,7 +489,8 @@ pub fn prepare_test_session(zargs string, folder string, oskipped []string, main
 			skipped << skipped_f
 		}
 		for skip_prefix in oskipped {
-			if f.starts_with(skip_prefix) {
+			skip_folder := skip_prefix + '/'
+			if fnormalised.starts_with(skip_folder) {
 				continue next_file
 			}
 		}

cmd/tools/vbuild-examples.v

@@ -12,7 +12,8 @@ const efolders = [
 fn main() {
 	args_string := os.args[1..].join(' ')
 	params := args_string.all_before('build-examples')
-	skip_prefixes := efolders.map(os.real_path(os.join_path_single(vroot, it)))
+	skip_prefixes := efolders.map(os.real_path(os.join_path_single(vroot, it)).replace('\\',
+		'/'))
 	res := testing.v_build_failing_skipped(params, 'examples', skip_prefixes, fn (mut session testing.TestSession) {
 		for x in efolders {
 			pathsegments := x.split_any('/')

cmd/tools/vbuild-tools.v

@@ -31,7 +31,7 @@ fn main() {
 	//
 	mut skips := []string{}
 	for stool in tools_in_subfolders {
-		skips << os.join_path(tfolder, stool)
+		skips << os.join_path(tfolder, stool).replace('\\', '/')
 	}
 	buildopts := args_string.all_before('build-tools')
 	mut session := testing.prepare_test_session(buildopts, folder, skips, main_label)