Fail when building Win64 from cygwin32

The gpgme libs need cross-arch windres support, which cygwin32
lacks.

Change-Id: Icbe013cf7983754e8b485dd7368cfc10f8fd0bcb
Reviewed-on: https://gerrit.libreoffice.org/45769Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>

configure.ac

@@ -10151,9 +10151,7 @@ fi
 AC_SUBST(ENABLE_PDFIUM)
 
 SYSTEM_GPGMEPP=
-if test "$_os" = "Linux" -o "$_os" = "Darwin" \
-   -o \( "$_os" = "WINNT" -a "$host_cpu" = "x86_64" \) \
-   -o \( "$_os" = "WINNT" -a "$host_cpu" = "i686" -a "$WINDOWS_SDK_ARCH" = "x86" \) ; then
+if test "$_os" = "Linux" -o "$_os" = "Darwin" -o "$_os" = "WINNT" ; then
     dnl ===================================================================
     dnl Check for system gpgme
     dnl ===================================================================
@@ -10180,6 +10178,8 @@ if test "$_os" = "Linux" -o "$_os" = "Darwin" \
         if test "$_os" != "WINNT"; then
             GPG_ERROR_LIBS="-L${WORKDIR}/UnpackedTarball/libgpg-error/src/.libs -lgpg-error"
             LIBASSUAN_LIBS="-L${WORKDIR}/UnpackedTarball/libassuan/src/.libs -lassuan"
+        elif test "$host_cpu" = "i686" -a "$WINDOWS_SDK_ARCH" = "x64"; then
+            AC_MSG_ERROR(gpgme cannot be built on cygwin32 for Win64.)
         fi
     fi
     ENABLE_GPGMEPP=TRUE