Ah ha! (Sort of...)
In the file <aolserver_root>/include/Makefile.global, I changed line #291 from 'TCL8X_LIB=libtcl8.3g.a' to 'TCL8X_LIB=libtcl83g.a' which seems to have gotten past the first error I mentioned.
However, now I'm seeing linker errors:
gcc -pthread -Wl,-E -o test test.o ../thread/libnsthread.a
ld: invalid command option `-E'
Checking the man pages for 'ld' under both Linux and OpenBSD that only the Linux linker (GCC, I assume) has the '-E' option which is the same as '--export-dynamic', but the OpenBSD 'ld' man page does not list '-E' as a valid option.
I see several '-B...' options such as '-Bdynamic'. If anyone has greater *BSD knowledge would this be a valid substitute? (Not such much that it would just compile, but is this overall a valid translation from a "linux" linker option to an "openbsd" linker option call?)
Thanks.