/usr/lib/petscdir/3.4.2/bin/petscarch is in libpetsc3.4.2-dev 3.4.2.dfsg1-8.1+b1.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2
#!/bin/sh -e echo linux-gnu-c-opt