fix: use bash from PATH in Makefile

[ironm00n]

/usr/bin/env is not present in all environments (ex. Nix sandbox)

[jpolitz]

I'm so confused. I swear I added this at either your request or @dbp 's (5fd829e)

[ironm00n]

That change was an improvement over /bin/bash since /usr/bin/env is a de-facto standard for unix-like systems.

However, not all build environments include a full filesystem hierarchy by default (as they aim to remain minimal). Relying on bash existing in $PATH is the most reliable solution here since it avoids assuming any fixed directory structures.

Due to the prevalence of shebangs, Nix (and other build systems), often patch #!/usr/bin/env ... to point to a static path (eg #!/nix/store/...). This doesn't work for Makefiles since its expected that it will use the environments dynamic $PATH.

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If you don't feel that this change is appropriate to upstream that's fine :). I will continue patching the Makefile in my own scripts.