Reinstantiate Cygwin function called `__getreent'

This partially reverts commit 10a30e7 as far as the Cygwin version of
the __getreent function is concerned.  Remove _COMPILING_NEWLIB guard
only allowing to use __getreent inline function when building newlib,
since we wan to use it in Cygwin as well.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
Signed-off-by: Stefan Assmann <sassmann@redhat.com>

winsup/cygwin/include/cygwin/config.h

@@ -35,7 +35,6 @@ extern "C" {
    compute these offsets already exists for the sake of gendef so
    we might as well just use it here.  */
 
-#ifdef _COMPILING_NEWLIB
 #ifdef __x86_64__
 #include "../tlsoffsets64.h"
 #else
@@ -52,7 +51,6 @@ extern inline struct _reent *__getreent (void)
 #endif
   return (struct _reent *) (ret + tls_local_clib);
 }
-#endif  /* _COMPILING_NEWLIB */
 
 #ifdef __x86_64__
 # define __SYMBOL_PREFIX

winsup/cygwin/thread.cc

@@ -80,6 +80,13 @@ pthread_mutex::no_owner()
     return res;
 }
 
+#undef __getreent
+extern "C" struct _reent *
+__getreent ()
+{
+  return &_my_tls.local_clib;
+}
+
 extern "C" void
 __cygwin_lock_init (_LOCK_T *lock)
 {