gdbm: Add generate-shim. Drop compile-bundle and install-bundle.

gdbm: Add generate-shim.  Drop compile-bundle and install-bundle.

LIAR/C's bundles cannot be built outside the core build tree.  So
compile-bundle is just e.g. compile.scm, and install-bundle is merged
with install-shim.  Generate-shim actually handles the whole process
from *.cdecl's to -shim.c and -const.bin, eliminating 4 tedious little
rules from every wrapper's Makefile.