Remove hard-coded value to patch W_CacheLumpNum

Lib/LibC.HC

@@ -1,7 +1,16 @@
+extern U64 get_symbol_address(U8 *entry_name);
+
 #define SEEK_SET 0
 #define SEEK_CUR 1
 #define SEEK_END 2
 
+U64 find_u32_in_memory(U64 offset, U32 value) {
+  I64 i = 0;
+  while (MemCmp(offset + i, &value, 4))
+    i++;
+  return offset + i;
+}
+
 U8 *f_whence[3];
 f_whence[0] = "SEEK_SET";
 f_whence[1] = "SEEK_CUR";
@@ -396,7 +405,9 @@ U0 lseek() {
 
 U8 *@mmap(I64 fd) {
   no_warn fd;
-  MemSetU32(0x4136ae, iwad_fp->data, 1);
+  MemSetU32(
+      find_u32_in_memory(get_symbol_address("W_CacheLumpNum"), 0xcafef00d),
+      iwad_fp->data, 1);
   return iwad_fp->data;
 }