fix tls_model autoconf test
It has an unused variable, so it was always failing (at least with gcc
4.9.1). Alternatively, the `-Werror` flag could be removed if it isn't
strictly necessary.
diff --git a/configure.ac b/configure.ac
index d221876..1d2e890 100644
--- a/configure.ac
+++ b/configure.ac
@@ -411,7 +411,7 @@
JE_CFLAGS_APPEND([-Werror])
JE_COMPILABLE([tls_model attribute], [],
[static __thread int
- __attribute__((tls_model("initial-exec"))) foo;
+ __attribute__((tls_model("initial-exec"), unused)) foo;
foo = 0;],
[je_cv_tls_model])
CFLAGS="${SAVED_CFLAGS}"