replace /bin/bash shebang with /usr/bin/env bash

[oliverlee]

This allows systems which don't have this location (e.g. NixOS) to run the scripts.

[oliverlee]

I suppose the failures are related to this, but I am not familiar with rules_rust:

toolchains_llvm/toolchain/osx_cc_wrapper.sh.tpl

Lines 165 to 167 in 0bdeae2

	# calling this script, which would make /usr/bin/ld unreachable. For example,
	# rules_rust does not set PATH (unless the user explicitly sets PATH in env
	# through attributes) [1] when calling rustc, and rustc does not replace an