Fix FORTIFY_SOURCE false positive

When -D_FORTIFY_SOURCE=2 was given during compilation,
sprintf and similar functions will check if their
first argument is in read-only memory and exit with
*** %n in writable segment detected ***
otherwise. To check if the memory is read-only, glibc
reads frpm the file "/proc/self/maps". If opening this
file fails due to too many open files (EMFILE), glibc
will now ignore this error.

Fixes [BZ #30932]

Signed-off-by: Volker Weißmann <volker.weissmann@gmx.de>
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

sysdeps/unix/sysv/linux/readonly-area.c

@@ -42,7 +42,9 @@ __readonly_area (const char *ptr, size_t size)
 	     to the /proc filesystem if it is set[ug]id.  There has
 	     been no willingness to change this in the kernel so
 	     far.  */
-	  || errno == EACCES)
+	  || errno == EACCES
+	  /* Process has reached the maximum number of open files.  */
+	  || errno == EMFILE)
 	return 1;
       return -1;
     }