188.8.131.52: differentiate cross-compiler output from target and host
No difference in the end-product, but seeing "x-compiling" in
build-logs makes them easier to read for slow people like me.
* while building the xc-host messages are from the host compiler.
If the host happens to be SBCL, that means:
; compiling (DEFUN FOO ...)
* while building the target:
; x-compiling (DEFUN FOO ...)
* while building CLOS and contribs on target: