Shell errors when building GCC 6.3 in parallel

[Matt Kline <matt at bitbashing dot io>]

My company has been using crosstool-NG for about a year now to build
cross-compilers for our embedded systems (largely ARM Cortex-M4 boards).
It's been invaluable - many thanks to everyone involved in the project.

We've been using GCC 6, and I'm trying to build the latest 6.3 bugfix release.
Building an x64 -> ARMv7 cross-compiler works fine, but I also need to build
x86 -> ARM compilers since a few of my coworkers still have 32-bit setups.[*]
I've had trouble with an x64->x86->ARM Canadian cross, so my approach so far
has been building the x86 toolchain in an i686 VM.

Oddly enough, when I run CT-NG in the VM (both the last release, 1.22.0, and
Git HEAD), I get some _really_ weird errors. Perusing the log,
it almost looks like there's some parse error in the shell scripts:

    [ALL  ]    /usr/bin/bash: line 2: : command not found
    [ALL  ]    /bin/sh: line 3: (cd ./zlib && : No such file or directory
    [ALL  ]    /bin/sh: line 4:   /usr/bin/make "DESTDIR=" ...  : File name too long
    [ALL  ]    /bin/sh: line 5: $'tall)': command not found

You can see some full logs at https://gist.github.com/mrkline/0a89952cd2f6284ae534fbd94b158f73

What's stranger still is that the problems go away if I set the number of
parallel jobs to 1, suggesting that it might be some concurrency problem.
Does anyone have suggestions as to what might be causing this?

FWIW, I'm on Arch Linux, which currently ships GCC 6.2.

Many thanks,

Matt Kline
Fluke Networks

[*]: We're working on fixing that ASAP, but until then...