Link to libjli, not libjvm, on macOS
Link to libjli, not libjvm, on macOS

When linking to Java on a macOS system without Apple Java 6 installed,
an error is given when attempting to load Java via JNI:

    No Java runtime present, requesting install.

And a dialog box appears saying "You need to install the legacy Java SE
6 runtime." Unfortunately, this is no longer possible on current
versions of macOS.

Linking to libjli sidesteps the issue, avoiding Apple's overzealous
linkage check, while still allowing access to Java's native API.

kivy/pyjnius,kivy/pyjnius,kivy/pyjnius