Issue with cross-compiling from intel macOS to arm64 macOS

[Eli S. Rykoff]

Hello-

The current version of ncurses 6.2 does not cross-compile correctly from intel 
macOS to arm64 macOS.  We have tracked this down to the following code snippet 
in the configure script:

if test "$cross_compiling" = yes ; then
    case $target_alias in
    (*-os2-emx*|*-msdosdjgpp*|*-cygwin*|*-msys*|*-mingw*|*-uwin*)
        cf_cv_mixedcase=no
        ;;
    (*)
        cf_cv_mixedcase=yes
        ;;
    esac
else
    rm -f conftest CONFTEST
    echo test >conftest
    if test -f CONFTEST ; then
        cf_cv_mixedcase=no
    else
        cf_cv_mixedcase=yes
    fi
    rm -f conftest CONFTEST
fi

The problem is that when compiling for darwin (*-darwin*) then this should set 
cf_cv_mixedcase=no, but instead it goes to the fallback cf_cv_mixedcase=yes.

Thanks,
-Eli Rykoff
Staff Scientist
SLAC National Accelerator Laboratory