Earlier versions of ltdl would look for extensions under $PWD; this
behavior changed in 2.2.6b.
* test-suite/standalone/Makefile.am (TESTS_ENVIRONMENT): Define
$builddir.
* test-suite/standalone/test-asmobs: Specify the full path to
`libtest-asmobs', using $builddir.
* test-suite/standalone/test-extensions: Likewise.