pkg/53508: lang/rust still fails with high -j values

[john%ziaspace.com@localhost]

>Number:         53508
>Category:       pkg
>Synopsis:       lang/rust still fails with high -j values
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Aug 10 17:15:00 +0000 2018
>Originator:     John Klos
>Release:        NetBSD 8.0
>Organization:
	
>Environment:
	
	
System: NetBSD dohee.nextvr.com 8.0_STABLE NetBSD 8.0_STABLE (DOHEE) #0: Tue Aug  7 22:48:23 UTC 2018  john%dohee.zia.io@localhost:/usr/obj-amd64/sys/arch/amd64/compile/DOHEE amd64
Architecture: amd64
Machine: amd64
>Description:
	
Attempting to compile rust from lang/rust fails with high -j values. Sometimes the 
rustc processes park, and sometimes they just chew CPU.

...
   Compiling proc_macro v0.0.0 
(file:///usr/pkgsrc/lang/rust/work/rustc-1.28.0-src/src/libproc_macro)
   Compiling syntax_ext v0.0.0 
(file:///usr/pkgsrc/lang/rust/work/rustc-1.28.0-src/src/libsyntax_ext)

22156 root      28    0   253M   43M CPU/15    19.4H 99.02% 99.02% rustc

This is on an 8 core AMD Ryzen.

>How-To-Repeat:
	
Compile lang/rust with -j 16
>Fix:
	
Compile with -j 1 or -j 2

>Unformatted: