Initialize PIC register for large PIC model C++ thunk

gcc/

	PR target/63815
	* config/i386/i386.c (ix86_init_large_pic_reg): New.  Extracted
	from ...
	(ix86_init_pic_reg): Here.  Use ix86_init_large_pic_reg.
	(x86_output_mi_thunk): Set PIC register to %r11.  Call
	ix86_init_large_pic_reg to initialize PIC register.

gcc/testsuite/

	PR target/63815
	* g++.dg/other/pr63815.C: New test.

From-SVN: r217445