fix gcc.dg/pr53849.c

[Mike Stump]

This test requires pthreads, so, I've copied bits from another testcase that 
uses -pthreads in the same way.

Checked it in.


diff --git a/gcc/testsuite/gcc.dg/pr53849.c b/gcc/testsuite/gcc.dg/pr53849.c
index 3b67010..eddc45f 100644
--- a/gcc/testsuite/gcc.dg/pr53849.c
+++ b/gcc/testsuite/gcc.dg/pr53849.c
@@ -1,4 +1,5 @@
 /* { dg-do compile } */
+/* { dg-require-effective-target pthread } */
 /* { dg-options "-O2 -ftree-parallelize-loops=2 -fno-tree-loop-im" } */
 
 extern int *b, *e[8], d;