Fixed typo spotted by Jeroen Witmond.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@9638 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/configure.in b/configure.in
index 2ea446b..ce7f9fd 100644
--- a/configure.in
+++ b/configure.in
@@ -909,7 +909,7 @@
 CFLAGS=$safe_CFLAGS
 
 AM_CONDITIONAL(HAVE_PTHREAD_CREATE_GLIBC_2_0,
-	       test x$ac_have_pthread_create_glibc_2_0 = yes)
+	       test x$ac_have_pthread_create_glibc_2_0 = xyes)
 
 
 # Check for eventfd_t, eventfd() and eventfd_read()