Make it possible build for WASM with --disable-gui, without Qt5

The various configury options here are a bit confusing, but this works
at least for me.

Change-Id: Ic9b04d40414d7d630d5a854295ce23b6e72a724a
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/143486
Tested-by: Jenkins
Reviewed-by: Thorsten Behrens <thorsten.behrens@allotropia.de>
diff --git a/configure.ac b/configure.ac
index 22589f7..c954d62 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1156,7 +1156,7 @@ emscripten)
    # API currently just exists in headers, not code
    usable_dlapi=no
    using_freetype_fontconfig=yes
    using_x11=no
    using_x11=yes
    test_openldap=no
    test_qt5=yes
    test_split_debug=yes
@@ -5429,7 +5429,7 @@ if test "$with_x" = "no"; then
    USING_X11=
fi

if test -z "$USING_X11" -a "$DISABLE_DYNLOADING" = TRUE -a "$enable_gen" = "yes"; then
if test -z "$USING_X11" -a "$enable_qt5" = "yes" -a "$enable_gen" = "yes"; then
    AC_MSG_ERROR([Can't select gen VCL plugin, if --without-x is used!])
fi