PR jit/64721: toplev: don't install signal-handlers when running within libgccjit

PR jit/64721: toplev: don't install signal-handlers when running within libgccjit

gcc/ChangeLog:
	PR jit/64721
	* main.c (main): Construct toplev instances with init_signals=true.
	* toplev.c (general_init): Add param "init_signals", and use it to
	conditionalize the calls to signal and host_hooks.extra_signals.
	(toplev::toplev): Add param "init_signals".
	(toplev::main): When invoking general_init, pass m_init_signals
	to control whether signal-handlers are installed.
	* toplev.h (toplev::toplev): Add param "init_signals".
	(toplev::m_init_signals): New field.

gcc/jit/ChangeLog:
	PR jit/64721
	* jit-playback.c (gcc::jit::playback::context::compile): Construct
	toplev instances with init_signals=false.

From-SVN: r220045