[flang] Fix crash in runtime-type-info.cpp

Recent work in runtime assignments failed an assertion in fir-dev
while running tests (flang/test/Semantics/defined-ops.f90).  This
test didn't fail in llvm-project/main because only the "new" Arm
driver is used now, and that only builds runtime derived type information
tables when some debug dumping options are enabled.

So add a reproducing test case to another test that is run with
-fdebug-dump-symbols, and fix the crash by emitting special procedure
binding information only for type-bound generic ASSIGNMENT(=) bindings
that are relevant to the runtime support library for use in intrinsic
assignment of derived types.

Differential Revision: https://reviews.llvm.org/D107918