Do not silently ignore an explicit --enable-sdremote-bluetooth

Change-Id: I362d9402f3123f852a4342ce5f8b604913e11ece
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/88762
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

configure.ac

@@ -10838,6 +10838,9 @@ if test -n "$enable_sdremote" -a "$enable_sdremote" != "no"; then
 
     if test $OS = MACOSX && test "$MACOSX_SDK_VERSION" -ge 101500; then
         # The Bluetooth code doesn't compile with macOS SDK 10.15
+        if test "$enable_sdremote_bluetooth" = yes; then
+            AC_MSG_ERROR([macOS SDK $with_macosx_sdk does not currently support --enable-sdremote-bluetooth])
+        fi
         enable_sdremote_bluetooth=no
     fi
     # If not explicitly enabled or disabled, default