openssl: Make build more robust by clearing some environment variables

[mkoeppe]

... in particular SYSTEM, set by our tox.ini, breaks the openssl build as seen in https://github.com/mkoeppe/sage/runs/1592276838:

  [openssl-1.1.1i]   Configuring openssl...
  [openssl-1.1.1i]   Operating system: x86_64-whatever-$(build/bin/sage-guess-package-system)
  [openssl-1.1.1i]   This system ($(build/bin/sage) is not supported. See file INSTALL for details.
  [openssl-1.1.1i]   Error configuring openssl.

CC: @sagetrac-tmonteil @kliem @dimpase

Component: packages: optional

Author: Matthias Koeppe

Branch/Commit: 5c169c7

Reviewer: Jonathan Kliem

Issue created by migration from https://trac.sagemath.org/ticket/31094

[mkoeppe]

Branch: u/mkoeppe/openssl__make_build_more_robust_by_clearing_some_environment_variables

[mkoeppe]

Commit: 5c169c7

[mkoeppe]

New commits:

5c169c7

build/pkgs/openssl/spkg-install.in: Unset some environment variables

[mkoeppe]

Author: Matthias Koeppe

[kliem]

Reviewer: https://github.com/kliem/sage/pull/31/checks

[mkoeppe]

comment:5

Build with this ticket merged went through in https://github.com/mkoeppe/sage/actions/runs/437548563 for #31082. Needs review

[mkoeppe]

comment:6

Still needs review, let's please get this in

[kliem]

comment:7

LGTM.

[kliem]

Changed reviewer from https://github.com/kliem/sage/pull/31/checks to Jonathan Kliem

[mkoeppe]

comment:8

Thanks!

[vbraun]

Changed branch from u/mkoeppe/openssl__make_build_more_robust_by_clearing_some_environment_variables to 5c169c7