The Semihosting v2 protocol requires us to output the Armv8-a HLT instruction
when in mixed mode (SEMIHOST_V2_MIXED_MODE), however it also requires this to
be done for Armv7-a and earlier architectures.
The HLT instruction is defined in the undefined encoding space for older
architectures but simulators such as QEMU already trap on it [1] for all
architectures and is a requirement for semihosting v2 [2].
Unfortunately the GAS restricts the use of HLT to Armv8-a which requires us to
use the instruction encodings we want directly in crt0.
This patch does this, I have not updated newlib/libc/* as that is quite out of
date already. A proper sync is needed in order to get things back in sync.
A different patch for this would be best.
[1] 19a6e31c9d
[2] https://developer.arm.com/docs/100863/latest/the-semihosting-interface
bfin - Analog Devices Blackfin processor.
sparc - Fujitsu Sparclite board. Works on the ex930, ex931, ex933
hp74x - Hewlett Packard HP742 board. Also some support for the hp743.
m68hc11 - Motorola 68HC11 or 68HC12 support.
m68k - Motorola MVME135 and IDP board. For CPU32 systems.
mep - Toshiba Media Processor.
pa - WinBond and Oki boards with a PA.
mips - R3000 support. Array Tech LSI33k based RAID disk controller.
lm32 - Lattice Mico32 simulator.
epiphany - Adapteva Epiphany multicore processor.
or1k - OpenRISC 1000 processor.
6d6a623e7d