tools/build/make.py: fix cross build on Fedora Linux

[alfredo]

Summary

Fedora defines shell functions for some commands used by FreeBSD build scripts,. Unortunatelly it makes them behave incorrectly for our purposes. For instance 'which which' returns:

which ()
{ 
    ( alias;
    eval ${which_declare} ) | /usr/bin/which --tty-only --read-alias --read-functions --show-tilde --show-dot $@
}

instead of

/usr/bin/which

This patch unsets those functions to restore original/expected behavior

Test Plan

On Fedora Linux:
$ MAKEOBJDIRPREFIX=~/obj tools/build/make.py TARGET=powerpc TARGET_ARCH=powerpc64 --cross-bindir=/usr/bin/ -j8 kernel-toolchain
$ MAKEOBJDIRPREFIX=~/obj tools/build/make.py TARGET=powerpc TARGET_ARCH=powerpc64 --cross-bindir=/usr/bin/ -j8 buildkernel

[imp]

Seems fine to me and reasonably paranoid....

[emaste]

OK with me

[arichardson]

This is fine as a workaround, but maybe we should just use command -v instead of which? I've seen build failures where docker images didn't include which

[alfredo]

In D36900#844037, @arichardson wrote:

This is fine as a workaround, but maybe we should just use command -v instead of which? I've seen build failures where docker images didn't include which

Hi @arichardson, I verified command -v which on Fedora and it also returns just "which" when the bash function is set.

Can we assume bash is mandatory for make.py? I found that we can have a clean bash environment with "env -i bash --noprofile --norc". One option would be cleanup bash at beginning and copy PATH var over. Another could be change the code that uses which to something like `env -i bash --noprofile --norc -c 'command -v <target_binary>".

[arichardson]

In D36900#844209, @alfredo wrote:

In D36900#844037, @arichardson wrote:

This is fine as a workaround, but maybe we should just use command -v instead of which? I've seen build failures where docker images didn't include which

Hi @arichardson, I verified command -v which on Fedora and it also returns just "which" when the bash function is set.

Can we assume bash is mandatory for make.py? I found that we can have a clean bash environment with "env -i bash --noprofile --norc". One option would be cleanup bash at beginning and copy PATH var over. Another could be change the code that uses which to something like `env -i bash --noprofile --norc -c 'command -v <target_binary>".

Sorry I should have been more explicit here, I meant "can we remove the dependency on which from the build system" (using command -v instead). If this is non-trivial I think this workaround is totally fine (or maybe remove all BASH_FUNC variables from the environment)