always turn return into __builtin_unreachable for noreturn fuctions [PR119599]

always turn return into __builtin_unreachable for noreturn fuctions [PR119599]

r8-3988-g356fcc67fba52b added code to turn return statements into __builtin_unreachable
calls inside noreturn functions but only while optimizing. Since -funreachable-traps
was added (r13-1204-gd68d3664253696), it is a good idea to move over to using
__builtin_unreachable (and the trap version with this option which defaults at -O0 and -0g)
instead of just a follow through even at -O0.

This also fixes a regression when inlining a noreturn function that returns at -O0 (due to always_inline)
as we would get an empty bb which has no successor edge instead of one with a call to __builtin_unreachable.

I also noticed there was no testcase testing the warning about __builtin_return inside a noreturn function
so I added a testcase there.

Bootstrapped and tested on x86_64-linux-gnu.

	PR ipa/119599

gcc/ChangeLog:

	* tree-cfg.cc (pass_warn_function_return::execute): Turn return statements always
	into __builtin_unreachable calls.

gcc/testsuite/ChangeLog:

	* gcc.dg/torture/pr119599-1.c: New test.
	* gcc.dg/builtin-apply5.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>