Allow gold to resolve defined TLS symbols in a PIE link.

This patch fixes Symbol::final_value_is_known so that a defined TLS symbol
in a PIE link is treated as having a known final value, thus allowing
GD->LE TLS optimization, eliminating an unnecessary GOT entry and dynamic
relocation.

gold/
	* symtab.cc (Symbol::final_value_is_known): Check for TLS symbol
	in a PIE link.
	* testsuite/Makefile.am (tls_pie_test.sh): New test.
	* testsuite/Makefile.in: Regenerate.
	* testsuite/tls_pie_test.sh: New.

gold/testsuite/tls_pie_test.sh

@@ -0,0 +1,58 @@
+#!/bin/sh
+
+# tls_pie_test.sh -- a test case for TLS symbols in PIE executables.
+
+# Copyright (C) 2015 Free Software Foundation, Inc.
+# Written by Cary Coutant <ccoutant@gmail.com>.
+
+# This file is part of gold.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+
+# This program 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 General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
+# MA 02110-1301, USA.
+
+# This file goes with tls_pie_test, a program compiled and linked
+# with -fpie -pie. Since TLS offsets are known at link time, even
+# in a PIE executable, we want to make sure that there are no
+# dynamic relocations for the TLS symbols.
+
+check()
+{
+    if ! grep -q "$2" "$1"
+    then
+	echo "Did not find expected output in $1:"
+	echo "   $2"
+	echo ""
+	echo "Actual output below:"
+	cat "$1"
+	exit 1
+    fi
+}
+
+check_missing()
+{
+    if grep -q "$2" "$1"
+    then
+	echo "Found unexpected output in $1:"
+	echo "   $2"
+	echo ""
+	echo "Actual output below:"
+	cat "$1"
+	exit 1
+    fi
+}
+
+check_missing tls_pie_test.stdout "o1 + 0"
+check_missing tls_pie_test.stdout "o2 + 0"
+check_missing tls_pie_test.stdout "o3 + 0"