Provide replacement value for PATH_MAX on platforms without it.

The buffer length is used in a static array returned from
Extra_FileNameGenericAppend(), used many places in the code, and a
more dynamic approach would require a huge refactoring.  There is no
guarantee that the 4096 value picked is large enough, but it matches
common values found on Linux.

src/misc/extra/extraUtilFile.c

@@ -23,6 +23,9 @@
 #define PATH_MAX MAX_PATH
 #else
 #include <limits.h>
+#  ifndef PATH_MAX
+#    define PATH_MAX 4096
+#  endif
 #endif
 
 #include "extra.h"