gdb/fortran: Add new 'info modules' command

gdb/fortran: Add new 'info modules' command

Add a new command 'info modules' that lists all of the modules GDB
knows about from the debug information.

A module is a debugging entity in the DWARF defined with
DW_TAG_module, currently Fortran is known to use this tag for its
modules.  I'm not aware of any other language that currently makes use
of DW_TAG_module.

The output style is similar to the 'info type' output:

    (gdb) info modules
    All defined modules:

    File info-types.f90:
    16:     mod1
    24:     mod2
    (gdb)

Where the user is told the file the module is defined in and, on the
left hand side, the line number at which the module is defined along
with the name of the module.

This patch is a new implementation of an idea originally worked on by
Mark O'Connor, Chris January, David Lecomber, and Xavier Oro from ARM.

gdb/ChangeLog:

	* dwarf2read.c (dw2_symtab_iter_next): Handle MODULE_DOMAIN.
	(dw2_expand_marked_cus): Handle MODULES_DOMAIN.
	(dw2_debug_names_iterator::next): Handle MODULE_DOMAIN and
	MODULES_DOMAIN.
	(scan_partial_symbols): Only create partial module symbols for non
	declarations.
	* psymtab.c (recursively_search_psymtabs): Handle MODULE_DOMAIN
	and MODULES_DOMAIN.
	* symtab.c (search_domain_name): Likewise.
	(search_symbols): Likewise.
	(print_symbol_info): Likewise.
	(symtab_symbol_info): Likewise.
	(info_modules_command): New function.
	(_initialize_symtab): Register 'info modules' command.
	* symtab.h (enum search_domain): Add MODULES_DOMAIN.
	* NEWS: Mention new 'info modules' command.

gdb/doc/ChangeLog:

	* gdb.texinfo (Symbols): Document new 'info modules' command.

gdb/testsuite/ChangeLog:

	* gdb.fortran/info-modules.exp: New file.
	* gdb.fortran/info-types.exp: Build with new file.
	* gdb.fortran/info-types.f90: Include and use new module.
	* gdb.fortran/info-types-2.f90: New file.

Change-Id: I2b781dd5a06bcad04620ccdc45f01a0f711adfad