LDSHARED needs to be [re]defined for packages that use distutils

[damianam]

The background of the problem is that when python gets built LDSHARED gets defined in $EBROOTPYTHON/lib/python2.7/_sysconfigdata.py. If it is not overridden, that's the value used. That works fine in most cases. However, when mixing compilers (building Python with GCCcore but pandas with icc), that doesn't work, as the linker is gcc, but using intel flags.

We should consider explicitely setting the following variables in PythonPackage.py:

• CC (already done)
• CXX (already done)
• OPT
• CFLAGS (already done)
• CCSHARED
• LDSHARED
• SO
• AR
• ARFLAGS

[boegel]

@damianam Makes sense, I wasn't aware that these variables are picked up from the 'host' Python...

It definitely makes sense to define these additional environment variables, ideally via prepare_step (i.e. where the toolchain build environment is being set up).

[marscher]

python/cpython#7914

[boegel]

We have an easy way now to fix $LDSHARED via check_ldshared = True in the easyconfig file (cfr. #1455), and we're looking into auto-fixing the value for recent Python versions in EasyBuild v4.0 (see #1788), so closing this...