builder: do not search for msvc when no need

vlib/v/builder/builder.v

@@ -59,13 +59,12 @@ pub fn new_builder(pref_ &pref.Preferences) Builder {
 	}
 	table.pointer_size = if pref_.m64 { 8 } else { 4 }
 	mut msvc := MsvcResult{}
-	$if windows {
-		msvc = find_msvc(pref_.m64) or {
-			if pref_.ccompiler == 'msvc' {
-				// verror('cannot find MSVC on this OS')
-			}
-			MsvcResult{
-				valid: false
+	if pref_.ccompiler == 'msvc' {
+		$if windows {
+			msvc = find_msvc(pref_.m64) or {
+				MsvcResult{
+					valid: false
+				}
 			}
 		}
 	}

vlib/v/builder/cc_windows.v

@@ -17,21 +17,24 @@ pub fn (mut v Builder) find_win_cc() ! {
 			println('failed command: `${cmd_version}`')
 			println('${v.pref.ccompiler} not found, looking for msvc...')
 		}
-		find_msvc(v.pref.m64) or {
-			if v.pref.is_verbose {
-				println('msvc not found, looking for thirdparty/tcc...')
-			}
-			thirdparty_tcc := os.join_path(v.pref.vroot, 'thirdparty', 'tcc', 'tcc.exe')
-			tcc_version_res := os.execute('${os.quoted_path(thirdparty_tcc)} -v')
-			if tcc_version_res.exit_code != 0 {
+		if !v.cached_msvc.valid {
+			msvc := find_msvc(v.pref.m64) or {
 				if v.pref.is_verbose {
-					println('tcc not found')
+					println('msvc not found, looking for thirdparty/tcc...')
+				}
+				thirdparty_tcc := os.join_path(v.pref.vroot, 'thirdparty', 'tcc', 'tcc.exe')
+				tcc_version_res := os.execute('${os.quoted_path(thirdparty_tcc)} -v')
+				if tcc_version_res.exit_code != 0 {
+					if v.pref.is_verbose {
+						println('tcc not found')
+					}
+					return error('tcc not found')
 				}
-				return error('tcc not found')
+				v.pref.ccompiler = thirdparty_tcc
+				v.pref.ccompiler_type = .tinyc
+				return
 			}
-			v.pref.ccompiler = thirdparty_tcc
-			v.pref.ccompiler_type = .tinyc
-			return
+			v.cached_msvc = msvc
 		}
 		v.pref.ccompiler = 'msvc'
 		v.pref.ccompiler_type = .msvc