configure: Test that gio libs from pkg-config work

On some hosts (eg Ubuntu Bionic) pkg-config returns a set of
libraries for gio-2.0 which don't actually work when compiling
statically. (Specifically, the returned library string includes
-lmount, but not -lblkid which -lmount depends upon, so linking
fails due to missing symbols.)

Check that the libraries work, and don't enable gio if they don't,
in the same way we do for gnutls.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200928160402.7961-1-peter.maydell@linaro.org

configure

@@ -3489,13 +3489,21 @@ if test "$static" = yes && test "$mingw32" = yes; then
 fi
 
 if $pkg_config --atleast-version=$glib_req_ver gio-2.0; then
-    gio=yes
     gio_cflags=$($pkg_config --cflags gio-2.0)
     gio_libs=$($pkg_config --libs gio-2.0)
     gdbus_codegen=$($pkg_config --variable=gdbus_codegen gio-2.0)
     if [ ! -x "$gdbus_codegen" ]; then
         gdbus_codegen=
     fi
+    # Check that the libraries actually work -- Ubuntu 18.04 ships
+    # with pkg-config --static --libs data for gio-2.0 that is missing
+    # -lblkid and will give a link error.
+    write_c_skeleton
+    if compile_prog "" "gio_libs" ; then
+        gio=yes
+    else
+        gio=no
+    fi
 else
     gio=no
 fi