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

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.