Demangle function names when disassembling

Demangle function names when disassembling

Andrew Burgess pointed out a regression, which he described in
PR symtab/26270:

================
After commit:

  commit bcfe6157ca288efed127c5efe21ad7924e0d98cf (refs/bisect/bad)
  Date:   Fri Apr 24 15:35:01 2020 -0600

      Use the linkage name if it exists

The disassembler no longer demangles function names in its output.  So
we see things like this:

  (gdb) disassemble tree_insert
  Dump of assembler code for function _Z11tree_insertP4nodei:
    ....

Instead of this:

  (gdb) disassemble tree_insert
  Dump of assembler code for function tree_insert(node*, int):
    ....

This is because find_pc_partial_function now returns the linkage name
rather than the demangled name.
================

This patch fixes the problem by introducing a new "overload" of
find_pc_partial_function, which returns the general_symbol_info rather
than simply the name.  This lets the disassemble command choose which
name to show.

Regression tested on x86-64 Fedora 32.

gdb/ChangeLog
2020-07-28  Tom Tromey  <tromey@adacore.com>

	PR symtab/26270:
	* symtab.h (find_pc_partial_function_sym): Declare.
	* cli/cli-cmds.c (disassemble_command): Use
	find_pc_partial_function_sym.  Check asm_demangle.
	* blockframe.c (cache_pc_function_sym): New global.
	(cache_pc_function_name): Remove.
	(clear_pc_function_cache): Update.
	(find_pc_partial_function_sym): New function, from
	find_pc_partial_function.
	(find_pc_partial_function): Rewrite using
	find_pc_partial_function_sym.

gdb/testsuite/ChangeLog
2020-07-28  Andrew Burgess  <andrew.burgess@embecosm.com>

	PR symtab/26270:
	* gdb.cp/disasm-func-name.cc: New file.
	* gdb.cp/disasm-func-name.exp: New file.