Having a list of very targeted suppressions allows us to still run the
majority of tests with valgrind checking, and not fail when Rust does
some trickery. This is for example the case with `std::sync::Once`
which uses `num_procs` calling out to the cgroups subsystem, sometimes
with a null path.
Suggested-by: Rusty Russell <@rustyrussell>
`valgrind` reports seems to flag some memory accesses that are ok in
the Rust standard library, which we can consider false positives for
our purposes:
```Valgrind error file: valgrind-errors.69147
==69147== Syscall param statx(file_name) points to unaddressable byte(s)
==69147== at 0x4B049FE: statx (statx.c:29)
==69147== by 0x2E2DA0: std::sys::unix::fs::try_statx (weak.rs:139)
==69147== by 0x2D7BD5: <std::fs::File as std::io::Read>::read_to_string (fs.rs:784)
==69147== by 0x2632CE: num_cpus::linux::Cgroup::param (linux.rs:214)
==69147== by 0x263179: num_cpus::linux::Cgroup::quota_us (linux.rs:203)
==69147== by 0x263002: num_cpus::linux::Cgroup::cpu_quota (linux.rs:188)
==69147== by 0x262C01: num_cpus::linux::load_cgroups (linux.rs:149)
==69147== by 0x26289D: num_cpus::linux::init_cgroups (linux.rs:129)
==69147== by 0x26BD88: core::ops::function::FnOnce::call_once (function.rs:227)
==69147== by 0x26B749: std::sync::once::Once::call_once::{{closure}} (once.rs:262)
==69147== by 0x139717: std::sync::once::Once::call_inner (once.rs:419)
==69147== by 0x26B6D5: std::sync::once::Once::call_once (once.rs:262)
==69147== Address 0x0 is not stack'd, malloc'd or (recently) free'd
==69147==
==69147== Syscall param statx(buf) points to unaddressable byte(s)
==69147== at 0x4B049FE: statx (statx.c:29)
==69147== by 0x2E2DA0: std::sys::unix::fs::try_statx (weak.rs:139)
==69147== by 0x2D7BD5: <std::fs::File as std::io::Read>::read_to_string (fs.rs:784)
==69147== by 0x2632CE: num_cpus::linux::Cgroup::param (linux.rs:214)
==69147== by 0x263179: num_cpus::linux::Cgroup::quota_us (linux.rs:203)
==69147== by 0x263002: num_cpus::linux::Cgroup::cpu_quota (linux.rs:188)
==69147== by 0x262C01: num_cpus::linux::load_cgroups (linux.rs:149)
==69147== by 0x26289D: num_cpus::linux::init_cgroups (linux.rs:129)
==69147== by 0x26BD88: core::ops::function::FnOnce::call_once (function.rs:227)
==69147== by 0x26B749: std::sync::once::Once::call_once::{{closure}} (once.rs:262)
==69147== by 0x139717: std::sync::once::Once::call_inner (once.rs:419)
==69147== by 0x26B6D5: std::sync::once::Once::call_once (once.rs:262)
==69147== Address 0x0 is not stack'd, malloc'd or (recently) free'd
==69147==
```
