libc: make common longjmp usable with NPTL

Call _longjmp_unwind conditionally under NPTL config option,
making longjmp usable with NPTL.

Signed-off-by: Filippo Arcidiacono <filippo.arcidiacono@st.com>
Signed-off-by: Carmelo Amoroso <carmelo.amoroso@st.com>

libc/sysdeps/linux/common/longjmp.c

@@ -24,7 +24,7 @@
 extern void __longjmp (__jmp_buf __env, int __val) attribute_noreturn;
 libc_hidden_proto(__longjmp)
 
-#if 0
+#ifdef __UCLIBC_HAS_THREADS_NATIVE__
 extern void _longjmp_unwind (jmp_buf env, int val);
 #endif
 
@@ -34,7 +34,7 @@ extern __typeof(longjmp) __libc_longjmp attribute_noreturn;
    call there to return VAL, or 1 if VAL is 0.  */
 void __libc_longjmp (sigjmp_buf env, int val)
 {
-#if 0
+#ifdef __UCLIBC_HAS_THREADS_NATIVE__
   /* Perform any cleanups needed by the frames being unwound.  */
   _longjmp_unwind (env, val);
 #endif