[gdb/symtab] Work around gas PR28629

[gdb/symtab] Work around gas PR28629

When running test-case gdb.tui/tui-layout-asm-short-prog.exp on AlmaLinux 9.2
ppc64le, I run into:
...
FAIL: gdb.tui/tui-layout-asm-short-prog.exp: check asm box contents
...

The problem is that we get:
...
    7              [ No Assembly Available ]
...
because tui_get_begin_asm_address doesn't succeed.

In more detail, tui_get_begin_asm_address calls:
...
		    find_line_pc (sal.symtab, sal.line, &addr);
...
with:
...
(gdb) p *sal.symtab
$5 = {next = 0x130393c0, m_compunit = 0x130392f0, m_linetable = 0x0,
  filename = "tui-layout-asm-short-prog.S",
  filename_for_id = "$gdb/build/gdb/testsuite/tui-layout-asm-short-prog.S",
  m_language = language_asm, fullname = 0x0}
(gdb) p sal.line
$6 = 1
...

The problem is the filename_for_id which is the source file prefixed with the
compilation dir rather than the source dir.

This is due to faulty debug info generated by gas, PR28629:
...
    <1a>   DW_AT_name        : tui-layout-asm-short-prog.S
    <1e>   DW_AT_comp_dir    : $gdb/build/gdb/testsuite
    <22>   DW_AT_producer    : GNU AS 2.35.2
...

The DW_AT_name is relative, and it's relative to the DW_AT_comp_dir entry,
making the effective name $gdb/build/gdb/testsuite/tui-layout-asm-short-prog.S.

The bug is fixed starting version 2.38, where we get instead:
...
    <1a>   DW_AT_name        :
             $gdb/src/gdb/testsuite/gdb.tui/tui-layout-asm-short-prog.S
    <1e>   DW_AT_comp_dir    : $gdb/build/gdb/testsuite
    <22>   DW_AT_producer    : GNU AS 2.38
...

Work around the faulty debug info by constructing the filename_for_id using
the second directory from the directory table in the .debug_line header:
...
 The Directory Table (offset 0x22, lines 2, columns 1):
  Entry	Name
  0	$gdb/build/gdb/testsuite
  1	$gdb/src/gdb/testsuite/gdb.tui
...

Note that the used gas contains a backport of commit 3417bfca676 ("GAS:
DWARF-5: Ensure that the 0'th entry in the directory table contains the
current working directory."), because directory 0 is correct.  With the
unpatched 2.35.2 release the directory 0 entry is incorrect: it's a copy of
entry 1.

Add a dwarf assembly test-case that reflects the debug info as generated by
unpatched gas 2.35.2.

Tested on x86_64-linux.

Approved-By: Tom Tromey <tom@tromey.com>