torture.at: Insulate more tests from buggy third-party m4 files.

torture.at: Insulate more tests from buggy third-party m4 files.

All tests that run autoreconf need to defend against the possibility
of aclocal not existing and/or barfing on bugs in third-party m4 files
installed on the build system.  Two of the “Missing auxiliary files”
tests were missing this defensive code.

 * tests/torture.at (Missing auxiliary files (install-sh))
   (Missing auxiliary files (foreign)): Prevent autoreconf from
   running aclocal.