stdbuf: Make itself executable library (libstdbuf)

[oech3]

Moved from #10395 (comment) . To support umasked /tmp with cargo install.

https://users.rust-lang.org/t/creating-an-executable-shared-library/95094

[Ecordonnier]

I don't understand what you mean. stdbuf uses the LD_PRELOAD mechanism, so having an executable shared library doesn't work.

[oech3]

File path to myself is easy to predict and always exist. We never see libstdbuf not found if `stdbuf` set itself to `LD_PRELOAD`.