For scripts, when we call fexecve(), on new kernels glibc calls execveat(),
which fails with ENOENT, and then we fall back to execve() which succeeds:
[pid 63039] execveat(3, "", ["/home/zbyszek/src/systemd/test/test-path-util/script.sh", "--version"], 0x7ffefa3633f0 /* 0 vars */, AT_EMPTY_PATH) = -1 ENOENT (No such file or directory)
[pid 63039] execve("/home/zbyszek/src/systemd/test/test-path-util/script.sh", ["/home/zbyszek/src/systemd/test/test-path-util/script.sh", "--version"], 0x7ffefa3633f0 /* 0 vars */) = 0
But on older kernels glibc (some versions?) implement a fallback which falls
into the same trap with bash $0:
[pid 13534] execve("/proc/self/fd/3", ["/home/test/systemd/test/test-path-util/script.sh", "--version"], 0x7fff84995870 /* 0 vars */) = 0
We don't want that, so let's call execveat() ourselves. Then we can do the
execve() fallback as we want.
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