init.sh: Provide more complete error info

On initialisation of the child instance, ./mk is
executed, but an error from it won't reveal what
command was actually executed.

This change makes that the case, since x_ does
print the command that caused an error.

This is useful for debugging. However, we don't
want x_ to cause a real exit, because we still
need to handle the lock file from the parent
instance.

Therefore, the first child instance is executed
inside a subshell, and xbmk_rval is set if that
subshell returns non-zero.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/init.sh

@@ -205,7 +205,7 @@ xbmk_child_init()
 	) || $err "Can't set up python symlink in $XBMK_CACHE/xbmkpath"
 
 	xbmk_rval=0
-	./mk "$@" || xbmk_rval=1
+	( x_ ./mk "$@" ) || xbmk_rval=1
 	rm -Rf "$xbmktmp" || xbmk_rval=1
 	rm -f lock || xbmk_rval=1
 	exit $xbmk_rval