patch 9.1.0837: cross-compiling has some issues

patch 9.1.0837: cross-compiling has some issues

Problem:  Cross-compiling to good modern operating systems is difficult as
          configure assumes obscure bugs are present by default. However,
          most core autoconf-based packages today assume features work
          when in doubt, making cross-compilation easier.
Solution: Assume features work by default and continue to issue a warning
          with the appropriate cache variable. This solution shifts the
          burden onto the users of rare buggy operating systems and
          makes cross-compilation work out of the box for everyone else.

The vim_cv_terminfo test was accidentally negated, where the yes case
was in the error handler, leading to false positives if the test program
failed to compile.

Split the timer_create detection into two phases: First locating the
the library containing timer_create, and then another check to check
if timer_create works to properly support cross-compilation.

Signed-off-by: Jonas 'Sortie' Termansen <sortie@maxsi.org>
Signed-off-by: Christian Brabandt <cb@256bit.org>