SWIG: move flat namespace flag for Python wrappings to its own variable

Description

• Document link to page in waveform review wiki why flag is needed for !2003 (merged)
• Keep EXTRA_SWIG_{OCTAVE,PYTHON}_LDFLAGS for arbitrary extra flags
• Also remove nonexistent SWIG_PYTHON_LIBS variable in lalinspiral/python/lalinspiral/Makefile.am

API Changes and Justification

Backwards Compatible Changes

• This change does not modify any class/function/struct/type definitions in a public C header file or any Python class/function definitions
• This change adds new classes/functions/structs/types to a public C header file or Python module

Backwards Incompatible Changes

• This change modifies an existing class/function/struct/type definition in a public C header file or Python module
• This change removes an existing class/function/struct/type from a public C header file or Python module

If any of the Backwards Incompatible check boxes are ticked please provide a justification why this change is necessary and why it needs to be done in a backwards incompatible way.

Review Status

cc @adam-mercer

requested review from @adam-mercer

assigned to @karl-wette

approved this merge request

enabled an automatic merge when the pipeline for 0028f4d5 succeeds

added apinone infra_autotools infra_swig lalinspiral labels

added 5 commits

• 59f27f0d...f65dcd8d - 3 commits from branch lscsoft:master
• 67b9cfd1 - SWIG: move flat namespace flag for Python wrappings to its own variable
• 09ed0235 - lalinspiral/python/lalinspiral/Makefile.am: remove nonexistent SWIG_PYTHON_LIBS

Compare with previous version

@adam-mercer Fixed an Autoconf/M4 quoting bug, platform macOS tests should now pass.

approved this merge request

enabled an automatic merge when the pipeline for a2095fdc succeeds

merged

mentioned in commit 2f58861f