berkeleydb: fix build of shared libraries

009d8fce and 0a5e5534 moved the --enable-static configure flag
from package files to the default _CONFIGURE_CMDS in
package/Makefile.autotools.in.
This broke Autotools packages that override _CONFIGURE_CMDS.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>