Fix building of many ports that use make from base, such as devel/apr1,
after r307676, which added transformation rules for .llo and .bco files.

These suffixes also have to be added the the global .SUFFIXES target,
otherwise the various suffix-transformation rules would be interpreted
as literal targets. E.g.,

.c.bco:
... commands ...

would actually to build a file named ".c.bco".