intel_adsp: Xtensa: Build failures on intel_adsp platforms with cadence clang toolchain

[gbarkadiusz]

Describe the bug
Build Failures on: intel_adsp/ace15_mtpm/sim, intel_adsp/ace20_lnl/sim, intel_adsp/ace_30/ptl/sim.

To Reproduce
Checkout to latest upstream (b1f9351)
Run: twister -p intel_adsp/ace15_mptm/sim -T tests/

Impact
Affects ACE platforms

Logs and console output

In file included from <path_to>/modules/lib/picolibc/newlib/libc/stdlib/nano-free.c:29:
<path_to>/modules/lib/picolibc/newlib/libc/stdlib/nano-malloc.h:60:9: error: unknown type name 'max_align_t'
typedef max_align_t align_chunk_t;
        ^
1 error generated.

Environment:

• OS: Linux
• Toolchain xt-clang
• Commit SHA or Version used (b1f9351)

Additional context
Bisect result: (843d661)

843d661b820e067f28112d2ea7dd822c2ecbcba2 is the first bad commit
commit 843d661b820e067f28112d2ea7dd822c2ecbcba2
Author: Keith Packard <keithp@keithp.com>
Date:   Thu Mar 27 15:03:06 2025 -0700

    modules: Update picolibc to version 1.8.10

    Switch to latest picolib release, version 1.8.10

    Signed-off-by: Keith Packard <keithp@keithp.com>

 west.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

[nashif]

@keith-packard any idea what is going on here?

[dcpleung]

Part of the issue is that picolibc does not inherent --std= from Zephyr build system, and defaults to C11. And xt-clang defaults to using XCC's pre-C11 headers by default, where max_align_t is not defined.

[keith-packard]

lmk if you want me to review any picolibc patches; the whole cmake build bits for that are purely in support of Zephyr, so if there are useful changes to be made, feel free.