pkg/54360: rust build broken on aarch64

[martin%NetBSD.org@localhost]

>Number:         54360
>Category:       pkg
>Synopsis:       rust build broken on aarch64
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Jul 09 06:50:00 +0000 2019
>Originator:     Martin Husemann
>Release:        NetBSD 8.99.50
>Organization:
The NetBSD Foundation, Inc.
>Environment:
System: NetBSD painkiller.duskware.de 8.99.50 NetBSD 8.99.50 (GENERIC64) #60: Sun Jul 7 10:06:33 CEST 2019 martin%seven-days-to-the-wolves.aprisoft.de@localhost:/work/src/sys/arch/evbarm/compile/GENERIC64 evbarm
Architecture: aarch64
Machine: evbarm
>Description:

Building rust fails reproducably for me (alas not very helpfull):

   Compiling unicode-width v0.1.5
   Compiling itoa v0.4.3
   Compiling build_helper v0.1.0 (/usr/pkgobj/lang/rust/work/rustc-1.36.0-src/src/build_helper)
error: Failed to delete invalidated or incompatible incremental compilation session directory contents `/usr/pkgobj/lang/rust/work/rustc-1.36.0-src/build/bootstrap/debug/incremental/build_helper-27nu7vz7cin0t/s-fdwun9l4ac-1mdckk7-working/dep-graph.bin`: No such file or directory (os error 2).

This happens when starting with a clean build.

>How-To-Repeat:
s/a

>Fix:
n/a