fix clang-20 warnign about string compare

clang-20 found spots where we were comparing pointers not string
contents.

Author: roblatham00

darshan-runtime/lib/darshan-stdio.c

@@ -228,11 +228,11 @@ extern int __real_fileno(FILE *stream);
     __rec_ref = darshan_lookup_record_ref(stdio_runtime->rec_id_hash, &__rec_id, sizeof(darshan_record_id)); \
     if(!__rec_ref) __rec_ref = stdio_track_new_file_record(__rec_id, __newpath); \
     if(!__rec_ref) { \
-        if(__newpath != (char*)__path) free(__newpath); \
+        if(strcmp(__newpath, (char*)__path) != 0 ) free(__newpath); \
         break; \
     } \
     _STDIO_RECORD_OPEN(__ret, __rec_ref, __tm1, __tm2, 1, -1); \
-    if(__newpath != (char*)__path) free(__newpath); \
+    if(strcmp(__newpath , (char*)__path) != 0) free(__newpath); \
     /* LDMS to publish realtime open tracing information to daemon*/ \
     if(dC.ldms_lib)\
         if(dC.stdio_enable_ldms)\