gcc: xtensa: make TARGET_HAVE_TLS definition static

gcc: xtensa: make TARGET_HAVE_TLS definition static

Remove TARGET_THREADPTR reference from TARGET_HAVE_TLS to avoid
static data initialization dependency on xtensa core configuration.

2020-06-15  Max Filippov  <jcmvbkbc@gmail.com>
gcc/
	* config/xtensa/xtensa.c (TARGET_HAVE_TLS): Remove
	TARGET_THREADPTR reference.
	(xtensa_tls_symbol_p, xtensa_tls_referenced_p): Use
	targetm.have_tls instead of TARGET_HAVE_TLS.
	(xtensa_option_override): Set targetm.have_tls to false in
	configurations without THREADPTR.