Use pkg-config to determine ncurses libs and cflags to use. Fixes when building
against ncurses with libtinfo split out.

--- pick-1.8.0/configure.ac
+++ pick-1.8.0/configure.ac
@@ -5,13 +5,10 @@
 AC_PROG_CC
 AM_PROG_CC_C_O
 AC_CHECK_FUNCS([pledge reallocarray strtonum])
-AC_SEARCH_LIBS([setupterm], [curses], [],
-  [
-    AC_SEARCH_LIBS([setupterm], [ncursesw],
-      [AC_DEFINE([HAVE_NCURSESW_H], [1], [Define if ncursesw is available])],
-      [AC_MSG_ERROR([unable to find setupterm function])]
-    )
-  ]
-)
+PKG_CHECK_MODULES([NCURSES], [ncursesw],
+  [AC_DEFINE([HAVE_NCURSESW_H], [1], [Define if ncursesw is available])],
+  [PKG_CHECK_MODULES([NCURSES], [ncurses])])
+CFLAGS="$CFLAGS $NCURSES_CFLAGS"
+LIBS="$LIBS $NCURSES_LIBS"
 AC_CONFIG_FILES([Makefile])
 AC_OUTPUT