`/proc` may not be mounted and its usage is [discouraged](https://wiki.freebsd.org/AvoidingLinuxisms) on BSDs. libstd [bundles](https://www.freebsd.org/doc/en/books/porters-handbook/bundled-libs.html) a C library from GCC into each executable. However, lang/gcc* don't expose sanitizers or Go runtime, so upstreaming is complicated. Let's just patch `/proc` out for downstream users.