deps: fix openssl assembly error on ia32 win32

`x86masm.pl` was mistakenly using .486 instruction set, why `cpuid` (and
perhaps others) are requiring .686 .
child_process: better error reporting for exec

Report path to executable and argv on error, stderr is not enough in
many cases.

fix #6796
configure: always set `arm_float_abi`

When not specified as a configure flag, and not derived from system
configuration, `arm_float_abi` should be set to `'default'`.

fix #6789