* libc/sys/arm/Makefile.am (extra_objs): Add _exit.o _nmi_isr.o
_fault_isr.o.
* libc/sys/arm/Makefile.in: Regenerated.
* libc/sys/arm/_exit.c: New file.
* libc/sys/arm/_fault_isr.c: Likewise.
* libc/sys/arm/_nmi_isr.c: Likewise.
* libc/sys/arm/configure.in (--enable-newlib-arm-v7m): New option.
* libc/sys/arm/configure:
* libc/sys/arm/crt0.S (_start): Do not use semihosting calls in
_start when configured for ARM V7M. Do not call
initialise_monitor_handles. Indent preprocessor directives.
(.isr_vector): New section, on ARM V7M.
* libc/sys/arm/swi.h (do_AngelSWI): New function.
* syscalls.c (_exit): Remove.
(do_AngelSWI): Likewise.
(CHECK_INIT): Remove.
(remap_handle): Call initialise_monitor_handles.
(__arm_monitor_handles_lock): New variable.
(initialise_monitor_handles): Make sure to run only once.
