dwarf2out: Emit DW_AT_location for global register vars during early dwarf [PR101905]

dwarf2out: Emit DW_AT_location for global register vars during early dwarf [PR101905]

The following patch emits DW_AT_location for global register variables
already during early dwarf, since usually late_global_decl hook isn't even
called for those, as nothing needs to be emitted for them.

2021-08-23  Jakub Jelinek  <jakub@redhat.com>

	PR debug/101905
	* dwarf2out.c (gen_variable_die): Add DW_AT_location for global
	register variables already during early_dwarf if possible.

	* gcc.dg/guality/pr101905.c: New test.

(cherry picked from commit b284053bb75661fc1bf13c275f3ba5364bb17608)