stdbuf: Support libstdbuf in same directory as stdbuf

[oech3]

If we published binaries from make build for refactoring CI *yml, it would load incorrect libstdbuf. @Ecordonnier

[Ecordonnier]

@oech3 are you working on this? I can send some PR

[oech3]

No. Because I'm not familiar with (lib)stdbuf...

[oech3]

Can uutils/stdbuf use GNU/libstdbuf.* ?

[Ecordonnier]

Can uutils/stdbuf use GNU/libstdbuf.* ?

in theory yes, but it would not really make sense. It is better to provide our own library so that uutils-stdbuf works standalone.