cmake: Fix CurlTests check for gethostbyname_r with 5 arguments

Fix the check code to pass 5 arguments instead of 6.  This typo was
introduced by commit aebfd4c (cmake: fix gethostby{addr,name}_r in
CurlTests, 2014-10-31).

CMake/CurlTests.c

@@ -139,7 +139,7 @@ int main(void)
   rc = gethostbyname_r(address, &h, &hdata);
 #elif defined(HAVE_GETHOSTBYNAME_R_5) || \
       defined(HAVE_GETHOSTBYNAME_R_5_REENTRANT)
-  rc = gethostbyname_r(address, &h, buffer, 8192, 0, &h_errnop);
+  rc = gethostbyname_r(address, &h, buffer, 8192, &h_errnop);
   (void)hp; /* not used for test */
 #elif defined(HAVE_GETHOSTBYNAME_R_6) || \
       defined(HAVE_GETHOSTBYNAME_R_6_REENTRANT)