x86-64: Don't set GLRO(dl_platform) to NULL [BZ #22299]

Since ld.so expands $PLATFORM with GLRO(dl_platform), don't set
GLRO(dl_platform) to NULL.

	[BZ #22299]
	* sysdeps/x86/cpu-features.c (init_cpu_features): Don't set
	GLRO(dl_platform) to NULL.
	* sysdeps/x86_64/Makefile (tests): Add tst-platform-1.
	(modules-names): Add tst-platformmod-1 and
	x86_64/tst-platformmod-2.
	(CFLAGS-tst-platform-1.c): New.
	(CFLAGS-tst-platformmod-1.c): Likewise.
	(CFLAGS-tst-platformmod-2.c): Likewise.
	(LDFLAGS-tst-platformmod-2.so): Likewise.
	($(objpfx)tst-platform-1): Likewise.
	($(objpfx)tst-platform-1.out): Likewise.
	(tst-platform-1-ENV): Likewise.
	($(objpfx)x86_64/tst-platformmod-2.os): Likewise.
	* sysdeps/x86_64/tst-platform-1.c: New file.
	* sysdeps/x86_64/tst-platformmod-1.c: Likewise.
	* sysdeps/x86_64/tst-platformmod-2.c: Likewise.

1 files changed, 23 insertions, 0 deletions

diff --git a/sysdeps/x86_64/tst-platformmod-2.c b/sysdeps/x86_64/tst-platformmod-2.c
new file mode 100644
index 0000000000..d0e5103892
--- /dev/null
+++ b/sysdeps/x86_64/tst-platformmod-2.c
@@ -0,0 +1,23 @@
+/* Test PRELOAD with $PLATFORM.
+   Copyright (C) 2017 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/>.  */
+
+int
+preload (void)
+{
+  return 0x1234;
+}