backport python38 wheels to release branch

Backport the changes to enable python38 wheels to the release branch.

➜  lalsuite git:(master) git show 77b318101e1af34b934548d682226dd7003f4cdf 
commit 77b318101e1af34b934548d682226dd7003f4cdf (HEAD -> master, upstream/master)
Merge: b526739757 0c0b4499fe
Author: Adam Mercer <adam.mercer@ligo.org>
Date:   Wed Dec 18 11:07:50 2019 -0600

    Merge branch 'python3.8-wheels' into 'master'
    
    Add python3.8 wheel builds
    
    Closes #212
    
    See merge request lscsoft/lalsuite!1023

➜  lalsuite git:(master) git log b526739757..0c0b4499fe
commit 0c0b4499fe5d964afe74904c48de7487a28c9476
Author: Duncan Macleod <duncan.macleod@ligo.org>
Date:   Tue Dec 17 09:58:20 2019 +0000

    lalinspiral: ignore GCC warnings from Python headers
    
    Co-authored-by: Leo Singer <leo.singer@ligo.org>

commit e01108ffb964b3fc084fb7f4d2647736a3b92b8c
Author: Duncan Macleod <duncan.macleod@ligo.org>
Date:   Mon Dec 16 11:24:55 2019 +0000

    lalburst: ignore GCC warnings from Python headers
    
    Co-authored-by: Leo Singer <leo.singer@ligo.org>

commit f4e50f5f4e50cc84f196572bdd38203c1ab38bb2
Author: Duncan Macleod <duncan.macleod@ligo.org>
Date:   Wed Oct 30 14:40:51 2019 +0000

    add python3.8 wheel builds
    
    fixes #212
➜  lalsuite git:(master)