Remove "extern int errno" from architectures/armv7-m/armv7-m.c
Remove "extern int errno" from architectures/armv7-m/armv7-m.c

since no all libc implement errno as an normal integer

Signed-off-by: Xiang Xiao <e94589cd03b1b3246d4b01f43c18f48c33b5de3a@xiaomi.com>
Change-Id: Ib2a27e29d6781d6f5dc5bb3c000eeceb7b0cd01b

adamgreen/mri,adamgreen/mri,adamgreen/mri