swig: fix incremental build in case of removed interface files

Commit v3.8.0-rc1~123^2 (UseSWIG: Automatically scan dependencies of SWIG files
for Makefiles, 2016-12-21) introduced automatic dependency scanning for files
`%include`d in a swig interface definition file. This works fine as long as no
such file is removed. But removing a dependent file breaks an incremental build
and `make` complains about a missing dependency, see #16830.

Integrate the approach proposed in the issue above into the SWIG-module, do the
workaround in a conditional step as it arises only for Makefile generators. For
other generators use the implementation before that commit.

Fixes: #17433.

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