Enable shared libopenconnect for Android build

We'll definitely want to use it from Java code for the authentication stage.
Not entirely sure yet how we'll invoke the main loop — perhaps by executing
the openconnect executable, but we *could* also invoke the main loop directly
from a Java process too. That might simplify the issue of protecting the
network sockets.

This ends up pulling libxml into libopenconnect.so, so the openconnect
executable gets it from there. Which isn't an ideal setup for the general
case but it's fairly convenient on Android.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

android/Makefile

@@ -248,7 +248,7 @@ $(OPENCONNECT_BUILD)/Makefile: $(GNUTLS_DEPS) $(LIBXML_DEPS) ../configure
 	mkdir -p $(OPENCONNECT_BUILD)
 	cd $(OPENCONNECT_BUILD) && ../../../configure $(CONFIGURE_ARGS) \
 	CFLAGS="--sysroot=$(NDK_SYSROOT) -DNO_BROKEN_DTLS_CHECK -DANDROID" \
-	GNUTLS_LIBS="$(shell PKG_CONFIG_LIBDIR=$(OC_SYSROOT)/lib/pkgconfig pkg-config --static --libs gnutls)"
+	GNUTLS_LIBS="$(shell PKG_CONFIG_LIBDIR=$(OC_SYSROOT)/lib/pkgconfig pkg-config --static --libs gnutls)" --enable-shared
 
 openconnect: $(OPENCONNECT_BUILD)/Makefile
 	make -C $(OPENCONNECT_BUILD)