[PATCH] configure: Test that gio libs from pkg-config work

[Peter Maydell]

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>
---
I wanted a statically-linked system emulation binary (which, yes,
I know is not really something we support :-)). I got one with
suitably liberal use of --disable-foo configure options, and
this was the only thing I couldn't work around that way.
The patch is needed because there's no --disable-gio. I suppose
we could add that instead (or as well)...
Possibly meson offers a nicer way to do this, but this was
simple and gnutls is doing the check this way already.
---
 configure | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/configure b/configure
index e8e8e984f24..cd79227d763 100755
--- a/configure
+++ b/configure
@@ -3762,13 +3762,21 @@ 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
-- 
2.20.1