dbus: Only use compile flags from valgrind, not libraries

Recent versions of valgrind have library code, which we don't need (or
want) to link to; all we actually want is <valgrind.h> and <memcheck.h>.

I had hoped that this would suppress the Requires.private when
generating our .pc file, but it doesn't seem to.

Signed-off-by: Simon McVittie <smcv@collabora.com>

dbus/meson.build

@@ -23,7 +23,7 @@ dbus_dependencies = [
     threads,
     network_libs,
     systemd,
-    valgrind,
+    valgrind.partial_dependency(compile_args: true),
 ]
 
 # source code that goes in the installed client library