i386: Fix up -fdollars-in-identifiers with identifiers starting with $ in -masm=att...

i386: Fix up -fdollars-in-identifiers with identifiers starting with $ in -masm=att [PR91298]

In AT&T syntax leading $ is special, so if we have identifiers that start
with dollar, we usually fail to assemble it (or assemble incorrectly).
As mentioned in the PR, what works is wrapping the identifiers inside of
parens, like:
	movl	$($a), %eax
	leaq	($a)(,%rdi,4), %rax
	movl	($a)(%rip), %eax
	movl	($a)+16(%rip), %eax
	.globl	$a
	.type	$a, @object
	.size	$a, 72
$a:
	.string	"$a"
	.quad	($a)
(this is x86_64 -fno-pic -O2).  In some places ($a) is not accepted,
like as .globl operand, in .type, .size, so the patch overrides
ASM_OUTPUT_SYMBOL_REF rather than e.g. ASM_OUTPUT_LABELREF.
I didn't want to duplicate what assemble_name is doing (following
transparent aliases), so split assemble_name into two parts; just
mere looking at the first character of a name before calling assemble_name
wouldn't be good enough, a transparent alias could lead from a name
not starting with $ to one starting with it and vice versa.

2020-01-22  Jakub Jelinek  <jakub@redhat.com>

	PR target/91298
	* output.h (assemble_name_resolve): Declare.
	* varasm.c (assemble_name_resolve): New function.
	(assemble_name): Use it.
	* config/i386/i386.h (ASM_OUTPUT_SYMBOL_REF): Define.

	* gcc.target/i386/pr91298-1.c: New test.
	* gcc.target/i386/pr91298-2.c: New test.