Linux: Add gettid system call wrapper [BZ #6399]

This commit adds gettid to <unistd.h> on Linux, and not to the
kernel-independent GNU API.

gettid is now supportable on Linux because too many things assume a
1:1 mapping between libpthread threads and kernel threads.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/posix/bits/unistd_ext.h b/posix/bits/unistd_ext.h
new file mode 100644
index 0000000000..d6e88f3bd4
--- /dev/null
+++ b/posix/bits/unistd_ext.h
@@ -0,0 +1,21 @@
+/* System-specific extensions of <unistd.h>, generic version.
+   Copyright (C) 2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _UNISTD_H
+# error "Never include <bits/unistd_ext.h> directly; use <unistd.h> instead."
+#endif