toolchain/53796: make prints wrong makefile path in an error message

[uwe%NetBSD.org@localhost]

>Number:         53796
>Category:       toolchain
>Synopsis:       make prints wrong makefile path in an error message
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    toolchain-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Dec 17 01:40:00 +0000 2018
>Originator:     Valery Ushakov
>Release:        NetBSD 8
>Organization:
>Environment:
>Description:
Make seems to mangle the path to an included makefile in an error message 
when that makefile contains an error.

>How-To-Repeat:
$ mkdir -p m/m/m/m
$ echo '.include "../../../../Makefile.inc"' > m/m/m/m/Makefile
$ cat > Makefile.inc
        error
default:
        echo hello world
^D
$ cd m/m/m/m
$ make
make: "../../../../../../../../Makefile.inc" line 1: Unassociated shell command "error"
make: Fatal errors encountered -- cannot continue

Note the the number of ".."s is double.

I've just stumbled into it with a current build, but I can see this bug
also on my -6 system.

>Fix: