Use builtin trap() to halt execution, rather than abort()

[ibuclaw]

This will, eg: emit .value 0x0b0f on x86, or .inst 0xe7f000f0 on ARM.

This should reduce the size of Druntime/Phobos ever so slightly, as there will be no more dependencies on libc abort().

	libgdruntime	libgphobos	helloworld
Before	5849kb	54.69mb	8569kb
After	5839kb	54.63mb	8560kb

So, is a subtle improvement.

[jpf91]

LGTM. Ready to merge?

[ibuclaw]

Yep it's ready. Up to you if we want to discuss the change in behaviour.

With abort, the halted program would raise a SIGABRT signal deep in the guts of libgcc.

Program received signal SIGABRT, Aborted.
0x00007ffff7109cc9 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
56      ../nptl/sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) bt
#0  0x00007ffff7109cc9 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
#1  0x00007ffff710d0d8 in __GI_abort () at abort.c:89
#2  0x0000000000403c9b in D main () at diemydarling.d:7

With this change, it instead raises a SIGILL signal at the exact point of the assert(0).

Program received signal SIGILL, Illegal instruction.
D main () at diemydarling.d:7

ARM and other targets might do something different, but at least they should guarantee halting the program.

[jpf91]

Sounds good.