AutoFDO: Implement streaming of file names from GCOV profile

AutoFDO: Implement streaming of file names from GCOV profile

This patch requires the changes from https://github.com/google/autofdo/pull/244
to work correctly.

Signed-off-by: Dhruv Chawla <dhruvc@nvidia.com>
gcc/ChangeLog:

	* auto-profile.cc (AUTO_PROFILE_VERSION): Bump to 3.
	(class function_instance_descriptor): New class.
	(get_normalized_path): New function.
	(string_table::~string_table): Update to free filenames.
	(string_table::vector_): Rename to ...
	(string_table::symbol_names_): ... this.
	(string_table::map_): Rename to ...
	(string_table::symbol_name_map_): ... this.
	(string_table::filenames_): New member.
	(string_table::filename_map_): Likewise.
	(string_table::symbol_to_filename_map_): Likewise.
	(string_table::get_index): Update to lookup symbol_name_map_.
	(string_table::get_name): Rename to ...
	(string_table::get_symbol_name): ... this.
	(string_table::add_name): Rename to ...
	(string_table::add_symbol_name): ... this.
	(string_table::get_filename): New function.
	(string_table::get_filename_by_symbol): Likewise.
	(string_table::get_filename_index): Likewise.
	(string_table::add_filename): Likewise.
	(string_table::read): Read file names from the GCOV profile.
	(function_instance::offline): Call
	get_function_instance_by_descriptor.
	(string_table::get_cgraph_node): Call get_symbol_name and
	symbol_name.
	(function_instance::get_function_instance_by_decl): Likewise.
	(function_instance::get_cgraph_node): Likewise.
	(function_instance::merge): Likewise.
	(match_with_target): Likewise.
	(function_instance::match): Likewise.
	(function_instance::dump): Likewise.
	(function_instance::dump_inline_stack): Likewise.
	(function_instance::find_icall_target_map): Likewise.
	(autofdo_source_profile::offline_unrealized_inlines): Likewise.
	(autofdo_source_profile::offline_external_functions): Likewise.
	(function_instance::read_function_instance): Likewise.
	(afdo_indirect_call):
	Also call find_function_instance, add_function_instance and
	remove_function_instance.
	(autofdo_source_profile::read): Likewise.
	(autofdo_source_profile::get_function_instance_by_decl): Call
	find_function_instance.
	(autofdo_source_profile::get_function_instance_by_name_index):
	Rename to ...
	(autofdo_source_profile::get_function_instance_by_descriptor):
	... this.
	(autofdo_source_profile::find_iter_for_function_instance): New
	function.
	(autofdo_source_profile::find_function_instance): Likewise.
	(autofdo_source_profile::add_function_instance): Likewise.
	(autofdo_source_profile::remove_function_instance): Likewise.