Log Message:
math/nickle: Make this cross-compile.

While here, because for CC_FOR_BUILD it was easiest to just edit
configure.ac and autoreconf anyway, move a configure patch to a
configure.ac patch for some readline symbol detection.

No change to generated file math-tables.5c (which is used only for
testing anyway) in native vs cross compilation.  `bmake test' passes
in native compilation.