build: Ubuntu defaults to --as-needed

configure.ac

@@ -203,7 +203,7 @@ esac
 
 AC_DEFUN([KNET_PKG_SONAME],[
 AC_MSG_CHECKING([for soname of $1])
-$CC -shared -nostdlib -o dummy.so $$1_LIBS
+$CC -shared -nostdlib -o dummy.so -Wl,--no-as-needed $$1_LIBS
 # Choosing the first SONAME is a best guess here:
 knet_pkg_soname=`$OBJDUMP -p dummy.so | $SED -n '/^Dynamic Section:$/,/^[^ ]/{s/ *NEEDED *//p;}' | head -n1`
 rm dummy.so