fix installation of Qt5 5.14.1 on top of zlib provided by Gentoo + stick to Python 2 as build dep

[boegel]

(created using eb --new-pr)

The patch fixes a compilation issue when using the zlib provided by Gentoo (when using --filter-deps=zlib):

In file included from ../../../3rdparty/assimp/contrib/unzip/ioapi.c:14:
../../../3rdparty/assimp/contrib/unzip/ioapi.h:38:44: error: expected =, ,, ;, asm or __attribute__ before OF
   38 | typedef voidpf (ZCALLBACK *open_file_func) OF((voidpf opaque, const char* filename, int mode));
      |

This is a known issue on Gentoo (see https://bugreports.qt.io/browse/QTBUG-68467), which is caused by a patch in zlib to rename the OF macro to _Z_OF (see also the long discussion in https://bugs.gentoo.org/383179).

The version change for the Python build dependency is because Python 2 is strictly required. If there's no python2 command available, the compilation of the qtwebengine component fails with:

make[2]: Entering directory '/tmp/vsc40023/easybuild/build/Qt5/5.14.1/GCCcore-9.3.0/qt-everywhere-src-5.14.1/qtwebengine/src'
/bin/sh: 1: Syntax error: "(" unexpected
make[2]: *** [Makefile:1095: errorbuild] Error 2

The corresponding line in the Makefile is this:

errorbuild: FORCE
        @echo Modules will not be built. Python version 2 (2.7.5 or later) is required to build QtWebEngine.

We only started using Python 3 as a build dep because we figured it was OK to do so, but we've only been testing on systems that still have python2 installed (which was not the case in the Gentoo environment I was hitting this problem in).

[boegel]

@boegelbot please test @ generoso

[boegelbot]

@boegel: Request for testing this PR well received on generoso

PR test command 'EB_PR=11385 EB_ARGS= /apps/slurm/default/bin/sbatch --job-name test_PR_11385 ~/boegelbot/eb_from_pr_upload_generoso.sh' executed!

• exit code: 0
• output:

Submitted batch job 7968

Test results coming soon (I hope)...

- notification for comment with ID 699153731 processed

Message to humans: this is just bookkeeping information for me,
it is of no use to you (unless you think I have a bug, which I don't).

[boegelbot]

Test report by @boegelbot
SUCCESS
Build succeeded for 1 out of 1 (1 easyconfigs in this PR)
generoso-x-4 - Linux centos linux 8.2.2004, x86_64, Intel(R) Xeon(R) CPU E5-2667 v3 @ 3.20GHz (haswell), Python 3.6.8
See https://gist.github.com/dbd0acc45f0807e717f07e4350c30e35 for a full test report.

[boegel]

Test report by @boegel
SUCCESS
Build succeeded for 1 out of 1 (1 easyconfigs in this PR)
node3406.kirlia.os - Linux centos linux 7.8.2003, x86_64, Intel(R) Xeon(R) Gold 6240 CPU @ 2.60GHz (cascadelake), Python 2.7.5
See https://gist.github.com/a380831eba1320cc14ddcf99f8966bb2 for a full test report.

[boegel]

Test report by @boegel
SUCCESS
Build succeeded for 1 out of 1 (1 easyconfigs in this PR)
node2661.swalot.os - Linux centos linux 7.8.2003, x86_64, Intel(R) Xeon(R) CPU E5-2660 v3 @ 2.60GHz (haswell), Python 2.7.5
See https://gist.github.com/48162eeed2bf7024e10e5b6f5a23e9ef for a full test report.

[zao]

Test report by @zao
SUCCESS
Build succeeded for 1 out of 1 (1 easyconfigs in this PR)
freja - Linux Ubuntu 20.04, x86_64, Intel(R) Core(TM) i7-8700K CPU @ 3.70GHz, Python 3.8.2
See https://gist.github.com/f4fef3844a5569c0f43055f6f66ba218 for a full test report.

[zao]

Cheated a bit with my test report (module-only) as I forgot to upload the test report twice. Build is solid.

[zao]

LGTM

[zao]

Going in, thanks @boegel!