'linux/limits.h' file not found breaking musl builds for c0.3.0

[cpswan]

Describe the bug

From the c0.3.0 (second attempt) build workflow where the musl builds fail with:

#9 30.91 [ 50%] Building C object _deps/atsdk-build/packages/atauth/CMakeFiles/atauth.dir/src/atauth_fetch_home_dir.c.o
#9 30.94 /sshnpd/sshnpd/build/_deps/atsdk-src/packages/atauth/src/atauth_fetch_home_dir.c:16:10: fatal error: 'linux/limits.h' file not found
#9 30.94    16 | #include <linux/limits.h>
#9 30.94       |          ^~~~~~~~~~~~~~~~
#9 30.94 1 error generated.

Steps to reproduce

1. First I merged chore: update atsdk version #1649 to deal with the previous build failure Compiler warnings preventing musl builds for c0.3.0 #1648
2. Then I re-release c0.3.0
3. And then the build failed for a new reason - progress :)

Expected behavior

Build completes successfully and we get a release with a complete set of binaries etc.

[XavierChanth]

Opened atsign-foundation/at_c#514 to address the issue

[cpswan]

@XavierChanth are you now going to repoint the at_c tag so that we can do another attempt at c0.3.0?

[XavierChanth]

Yes, I also want the atdirectory fix changes included

[XavierChanth]

@cpswan can this be closed? This should be fixed in the latest build, I put conditionals in place to only include that header when it exists (otherwise we pick some sane fallback values for the constants we need from it)