[src/erc32] Use ncurses instead of termcap on Cygwin too

[src/erc32] Use ncurses instead of termcap on Cygwin too

This removes a Cygwin-specific libtermcap hack that was dependent on
the presence of one of the multiple alternative libraries.  The one it
was hard-coded to pick isn't included with Cygwin anymore.

According to Corinna, libtermcap was removed from Cygwin a long time
ago, and libncurses is used in Cygwin for a long time too.

The fix is to make Cygwin use the same autoconf code to figure out the
correct lib as any other target.

sim/erc32/Changelog:
2018-10-30  Joel Sherrill <joel@rtems.org>

	* configure.ac: Remove the Cygwin-specific libtermcap.a hack
	and use the standard logic to determine which library to use.
	* configure: Regenerate.