Support embedding the driver in-process within libgccjit

Support embedding the driver in-process within libgccjit

gcc/ChangeLog:
	* gcc-main.c (main): Add params to driver ctor.
	* gcc.c (class env_manager): New.
	(env): New global.
	(env_manager::init): New.
	(env_manager::get): New.
	(env_manager::xput): New.
	(env_manager::restore): New.
	Poison getenv and putenv.
	(DEFAULT_TARGET_SYSTEM_ROOT): New.
	(target_system_root): Update initialization to use
	DEFAULT_TARGET_SYSTEM_ROOT.
	(struct spec_list): Add field "default_ptr".
	(INIT_STATIC_SPEC): Initialize new field "default_ptr".
	(init_spec): Likewise.
	(set_spec): Clear field "default_ptr".
	(read_specs): Free "spec" and "buffer".
	(xputenv): Reimplement in terms of env_manager.
	(process_command): Replace ::getenv calls with calls to the
	env_manager singleton.
	(process_brace_body): Free string in three places.
	(driver::driver): New.
	(driver::~driver): New.
	(used_arg): Convert from a function to...
	(class used_arg_t): ...this class, and...
	(used_arg): ...this new global instance.
	(used_arg_t::finalize): New function.
	(getenv_spec_function): Add "const" to local "value".  Replace
	::getenv call with call to the env_manager singleton.
	(path_prefix_reset): New function.
	(driver::finalize): New function.
	* gcc.h (driver::driver): New.
	(driver::~driver): New.
	(driver::finalize): New.

gcc/jit/ChangeLog:
	* docs/cp/topics/contexts.rst
	(gccjit::context::set_bool_use_external_driver): New.
	* docs/internals/test-hello-world.exe.log.txt: Update.
	* docs/topics/compatibility.rst (LIBGCCJIT_ABI_5): New.
	* docs/topics/contexts.rst
	(gcc_jit_context_set_bool_use_external_driver): New.
	* jit-common.h (enum inner_bool_option): Add
	INNER_BOOL_OPTION_USE_EXTERNAL_DRIVER.
	* jit-playback.c (gcc_driver_name): New global.
	(gcc:jit::playback::context::invoke_driver): Split out second
	half into...
	(gcc::jit::playback::context::invoke_embedded_driver): ...this new
	function, and...
	(gcc::jit::playback::context::invoke_external_driver): ...this new
	function.
	* jit-playback.h
	(gcc::jit::playback::context::get_inner_bool_option): New.
	(gcc::jit::playback::context::invoke_embedded_driver): New.
	(gcc::jit::playback::context::invoke_external_driver): New.
	* jit-recording.c (inner_bool_option_reproducer_strings):
	Add entry for INNER_BOOL_OPTION_USE_EXTERNAL_DRIVER.
	* libgccjit++.h
	(gccjit::context::set_bool_use_external_driver): New.
	* libgccjit.c (gcc_jit_context_set_bool_use_external_driver): New.
	* libgccjit.h (gcc_jit_context_set_bool_use_external_driver): New.
	(LIBGCCJIT_HAVE_gcc_jit_context_set_bool_use_external_driver):
	New.
	* libgccjit.map (LIBGCCJIT_ABI_5): New.
	* notes.txt: Show invocation of embedded copy of driver.
	* docs/internals/test-hello-world.exe.log.txt: Update

gcc/testsuite/ChangeLog:
	* jit.dg/test-error-pr63969-missing-driver.c: Add call to
	gcc_jit_context_set_bool_use_external_driver.

From-SVN: r227188