Revision 1915235

swig-rb: Block SWIG 4.2.0 before building Ruby bindings

SWIG Ruby bindings cannot build with SWIG 4.2.0 because it produces
a broken external runtime code[1]. So we note it is broken and
block users from building swig-rb with it.

[1] https://github.com/swig/swig/issues/2751

* build/ac-macros/swig.m4
  (SVN_FIND_SWIG): Check SWIG 4.2.0 and block it for swig-rb.
* subversion/bindings/swig/INSTALL
  (BUILDING SWIG BINDINGS FOR SVN ON UNIX, Step 1):
   Note that SWIG 4.2.0 is broken for Ruby.

Reported by: @jplesnik on Github,
             jun66j5