Work around newlib compilation failure with clang-15

[gulmezmerve]

The command ./cheribuild.py newlib-baremetal-riscv64-purecap -d currently fails when using clang-15.

This issue has been reported multiple times on the Cheri Slack channel.

As a workaround, this commit adds the -Wno-implicit-function-declaration option to suppress these errors. While this may not be a permanent fix, it should unblock users and help others facing the same problem.

[heshamelmatary]

Hi Merve,

I have pending PRs for both newlib [1] and cheribuild [2] to be able to build with latest toolchain with master cheribuild.

[1] CTSRD-CHERI/newlib#6
[2] #416

[gulmezmerve]

Thanks! It was a long-running problem that people struggled with. I hope this will finally solve it.

[heshamelmatary]

Thanks! It was a long-running problem that people struggled with. I hope this will finally solve it.

@gulmezmerve Meanwhile you can probably checkout the newlib branch on the PR and try to build it and report back to us here if it works for you

[gulmezmerve]

@heshamelmatary yes, I tested it with the cheribuild branch freertos-hkma2-merge and the newlib branch merge-newlib-4.5.0. It works on my side!

[arichardson]

I think we can merge this trivial fix - your PR is rather invasive and needs some time for review.

[gulmezmerve]

Yeah I agree with @arichardson

We already provided this small trick to Ericsson, KU Leuven, and the University of Waterloo.
Maybe it’s time to merge 😅

[arichardson]

CI failure is unrelated, merging