Move the rust "{" hack

Move the rust "{" hack

The DWARF reader has a special case to work around a bug in some
versions of the Rust compiler -- it ignores mangled names that contain
a "{" character.

I noticed that this check should probably be in dw2_linkage_name
rather than only in dwarf2_physname.  The former is called in some
cases that the latter is not.

Also, I noticed that this work is not done for the partial DIE reader,
so this patch adds the check there as well.

gdb/ChangeLog
2020-04-24  Tom Tromey  <tom@tromey.com>

	* dwarf2/read.c (dw2_linkage_name): Move Rust "{" hack here...
	(dwarf2_physname): ... from here.
	(partial_die_info::read): Add Rust "{" hack.