util: add util_strdup() wrapper macro

To work around MSVC warning that strdup() is a deprecated POSIX function.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

src/util/u_string.h

@@ -203,6 +203,7 @@ util_strstr(const char *haystack, const char *needle)
 
 
 #define util_strcasecmp stricmp
+#define util_strdup _strdup
 
 #else
 
@@ -217,6 +218,7 @@ util_strstr(const char *haystack, const char *needle)
 #define util_strncat strncat
 #define util_strstr strstr
 #define util_strcasecmp strcasecmp
+#define util_strdup strdup
 
 #endif