dl: minor improvement of get_shared_library_extension (#9070)

vlib/dl/dl.v

@@ -9,14 +9,13 @@ pub const (
 // i.e. .dll on windows, .so on most unixes, .dylib on macos.
 [inline]
 pub fn get_shared_library_extension() string {
-	mut res := '.so'
-	$if macos {
-		res = '.dylib'
+	return $if windows {
+		'.dll'
+	} $else $if macos {
+		'.dylib'
+	} $else {
+		'.so'
 	}
-	$if windows {
-		res = '.dll'
-	}
-	return res
 }
 
 // get_libname returns a library name with the operating system specific extension for