Ruby 1.9.3 fails to compile with tcl/tk on s390x
When compiling Ruby 1.9.3 on s390x without specifying --libdir for configure, tcl/tk extension fails to build: Fail to find [tclConfig.sh, tkConfig.sh].
This is caused by erroneous function maybe_64bit? in ext/tk/extconf.rb, which doesn't recognize s390x as 64 bit architecture.
Proposed fix is in attached file.