Intel Hex flashing time increase in latest micro:bit builds

[microbit-carlos]

Intel Hex flashing time has increased in the main branch with armcc compared with the micro:bit factory release from commit 1436bdcc67029fdfc0ff03b73e12045bb6a9f272.

The measurements below have been done in macOS 11 with rsync and this Intel Hex file: ihex-v2-upy.hex.zip For comparison I've also added a snapshot of the develop branch with armcc and GCC.

Build	Flashing time (s)
armc 1436bdc (255)	~13.5
armcc main 8509fea	~16.6
armcc develop 930ef1df	~16.5
GCC develop 930ef1df	~17.5

I've only run this on a micro:bit V2, so it's possible this might affect other ports as well, but I haven't tested it.

[mathias-arm]

My tests show very similar results except for the v0255 value which is for me in line with the other armcc tests.