x/build: add a linux/i386 builder without `COMPAT_32BIT_TIME` Kconfig set

I am reviewing a CL https://go-review.googlesource.com/c/go/+/701615 that aims to fix a bug (#75133) where the go runtime stopped working on 32 bits linux systems unless a compatibility Kconfig flag is set.

Could we please get a builder where this flag is unset (`COMPAT_32BIT_TIME=n`) ?