Build system races when doing make install debug

[maleadt]

When accidentally doing a make install debug I ran into mysterious checksum issues:

$ git clone ... julia
$ $ make -C julia -j install debug
make[3]: Entering directory '/tmp/julia/deps'
===============================================================================
  ERROR: sha512 checksum failure on p7zip.v16.2.0-1.x86_64-linux-gnu.tar.gz, should be:
===============================================================================
  ERROR: sha512 checksum failure on OpenLibm.v0.7.0-0.x86_64-linux-gnu.tar.gz, should be:
100  380k  100  380k    0     0   218k      0  0:00:01  0:00:01 --:--:-- 1081k
make[3]: Leaving directory '/tmp/julia/stdlib'
100  187k  100  187k    0     0   127k      0  0:00:01  0:00:01 --:--:--  586k
      fdc322926de636060699daf87dd69003e092a10cc7125a0963a94fa588f0af95
      79f495b9a5332eabae4742cd6f5233403f69ffb30e6fff30d8dee5cc10e4a278
      62dd5da2adcf6aa4fdf74e1c01ab46c25ff5e36c6f5665a1781a8b8240ac5624
  But `sha512sum /tmp/julia/deps/srccache/p7zip.v16.2.0-1.x86_64-linux-gnu.tar.gz | awk '{ print $1; }'` results in:
===============================================================================
  ERROR: sha512 checksum failure on Pkg-8c415b01924eb4452cb7be8438c2bbc0978d1152.tar.gz, should be:
      e9e00c82fc32936a4b42e3446ecad208a96fbfe2b2e9d91db15b52195f5e1fe8
  But `sha512sum /tmp/julia/deps/srccache/OpenLibm.v0.7.0-0.x86_64-linux-gnu.tar.gz | awk '{ print $1; }'` results in:
      3e6106c058ca779e27172acb89608942d47402f50326727124b7c784ef07e1b6
      3f6292b2b7d7f3593e97ac18175c2829c438ce677be86a799c83ec553c0d4d9e
      c389d561f16ee3b77fd1bd38708d704145110d53c858233fc8cc11a5c7af44cf
  This can happen due to bad downloads or network proxies, please check your
  network proxy/firewall settings and delete
      fddf8f859ff82b1fe89b5c2745d6ea445743bf66eb5894881c5618349e568539
  This can happen due to bad downloads or network proxies, please check your
  network proxy/firewall settings and delete
  /tmp/julia/deps/srccache/p7zip.v16.2.0-1.x86_64-linux-gnu.tar.gz
  to force a redownload when you are ready
===============================================================================
make[1]: *** [/tmp/julia/deps/p7zip.mk:64: /tmp/julia/usr/manifest/p7zip] Error 2
make[1]: *** Waiting for unfinished jobs....
      576ad34eed41d4749fc4a2b263bf6a75d2224d8ac0672b5e3f52666e9fa5c4c9
      a3565498402f9b611543376c2a1f37cb8a1414095e6e9a76ba9331ef52483fe1
  But `sha512sum /tmp/julia/stdlib/srccache/Pkg-8c415b01924eb4452cb7be8438c2bbc0978d1152.tar.gz | awk '{ print $1; }'` results in:
  /tmp/julia/deps/srccache/OpenLibm.v0.7.0-0.x86_64-linux-gnu.tar.gz
  to force a redownload when you are ready
===============================================================================
100  392k  100  392k    0     0   263k      0  0:00:01  0:00:01 --:--:-- 1142k
make[1]: *** [/tmp/julia/deps/openlibm.mk:38: /tmp/julia/usr/manifest/openlibm] Error 2
      78738de646512fa5eabfab7102ff5a5f8ad4892def202324206024c4ae746c0f
      856cd31ad508622c98783e584d760f80b685a5781ed53a8767c97b4fc89aa383
  This can happen due to bad downloads or network proxies, please check your
  network proxy/firewall settings and delete
  /tmp/julia/stdlib/srccache/Pkg-8c415b01924eb4452cb7be8438c2bbc0978d1152.tar.gz
  to force a redownload when you are ready
===============================================================================
make[1]: *** [Makefile:27: Pkg-8c415b01924eb4452cb7be8438c2bbc0978d1152/source-extracted] Error 2
make[1]: Leaving directory '/tmp/julia/stdlib'

Maybe this can be classified as "unsupported", but it's good to have some reference to this in the bug tracker anyway.