Rename variable for C23.

--- adflib-0.7.12/examples/unadf.c	2025-07-04 17:21:56.631746648 +0100
+++ adflib-0.7.12/examples/unadf.c	2025-07-04 17:21:49.832271086 +0100
@@ -517,7 +517,7 @@
     struct Volume *vol;
     struct List *list, *cell;
     int volNum;
-    BOOL true = TRUE;
+    BOOL trueVal = TRUE;
 
     if (argc<2) {
         help();
@@ -655,7 +655,7 @@
     }
 
     if (cflag && isDIRCACHE(vol->dosType) && lflag) {
-        adfChgEnvProp(PR_USEDIRC,&true);
+        adfChgEnvProp(PR_USEDIRC,&trueVal);
         if (!qflag)
             puts("Using dir cache blocks.");
     }