newlib/.../getreent.c: Allow to be provided by host and do so for RTEMS

RTEMS provides the option to have a global or per-thread reentrancy
as part of application configuration. As part of this, RTEMS provides
the implementation of __getreent() as appropriate. Allow the target
to determine if this method is present in libc.a.

newlib/configure.host

@@ -586,7 +586,7 @@ case "${host}" in
 	default_newlib_io_long_double="yes"
 	default_newlib_io_pos_args="yes"
 	CC="${CC} -I${cygwin_srcdir}/include"
-	newlib_cflags="${newlib_cflags} -DHAVE_OPENDIR -DHAVE_RENAME -DSIGNAL_PROVIDED -D_COMPILING_NEWLIB -DHAVE_BLKSIZE -DHAVE_FCNTL -DMALLOC_PROVIDED"
+	newlib_cflags="${newlib_cflags} -DHAVE_OPENDIR -DHAVE_RENAME -DGETREENT_PROVIDED -DSIGNAL_PROVIDED -D_COMPILING_NEWLIB -DHAVE_BLKSIZE -DHAVE_FCNTL -DMALLOC_PROVIDED"
 	syscall_dir=syscalls
 	;;
   *-*-phoenix*)
@@ -605,7 +605,7 @@ case "${host}" in
 	default_newlib_io_long_long="yes"
 	default_newlib_io_c99_formats="yes"
 	newlib_cflags="${newlib_cflags} -D_COMPILING_NEWLIB"
-	newlib_cflags="${newlib_cflags} -DCLOCK_PROVIDED -DMALLOC_PROVIDED -DEXIT_PROVIDED -DSIGNAL_PROVIDED -DREENTRANT_SYSCALLS_PROVIDED -DHAVE_NANOSLEEP -DHAVE_BLKSIZE -DHAVE_FCNTL -DHAVE_ASSERT_FUNC"
+newlib_cflags="${newlib_cflags} -DCLOCK_PROVIDED -DMALLOC_PROVIDED -DEXIT_PROVIDED -DSIGNAL_PROVIDED -DGETREENT_PROVIDED -DREENTRANT_SYSCALLS_PROVIDED -DHAVE_NANOSLEEP -DHAVE_BLKSIZE -DHAVE_FCNTL -DHAVE_ASSERT_FUNC"
         # turn off unsupported items in posix directory 
 	newlib_cflags="${newlib_cflags} -D_NO_GETLOGIN -D_NO_GETPWENT -D_NO_GETUT -D_NO_GETPASS -D_NO_SIGSET -D_NO_WORDEXP -D_NO_POPEN -D_NO_POSIX_SPAWN"
 	;;

newlib/libc/reent/getreent.c

@@ -1,5 +1,11 @@
 /* default reentrant pointer when multithread enabled */
 
+#ifdef GETREENT_PROVIDED
+
+int _dummy_getreent;
+
+#else
+
 #include <_ansi.h>
 #include <reent.h>
 
@@ -12,3 +18,5 @@ _DEFUN_VOID(__getreent)
 {
   return _impure_ptr;
 }
+
+#endif