Fix UTF-8 flag detection regex

Updated the regular expression for detecting the /utf-8 compiler flag to be case-insensitive for each character, ensuring proper detection regardless of case.

Author: Mzying2001

sw/CMakeLists.txt

@@ -23,7 +23,7 @@ if(MSVC)
     # 检查是否已存在/utf-8
     if(_opts)
         foreach(opt IN LISTS _opts)
-            if(opt MATCHES "(?i)/utf-8")
+            if(opt MATCHES "/[Uu][Tt][Ff]-8")
                 set(_has_utf8 TRUE)
                 break()
             endif()