* automake.in (require_build_directory): New function, extracted

* automake.in (require_build_directory): New function, extracted
from ...
(handle_single_transform_list): ... here.
(require_build_directory_maybe): New function.
(handle_prograns, handle_libraries, handle_ltlibraries): Call
require_build_directory_maybe() to ensure the subdirectory
in which a target may lie will exist when the target is created.
(handle_libraries, handle_ltlibraries): Use basename before
checking library name.
* lib/am/library.am (%LIBRARY%): Depend on %DIRSTAMP%.
* lib/am/ltlibrary.am (%LTLIBRARY%): Likewise.
* lib/am/program.am (%PROGRAM%): Likewise.