Fix Darwin builds for non-standard environments (e.g. Nix)

[martinjlowm]

Issues:

Not reported.

Description of changes:

aws-ls-sys fails to build via Nix (crate2nix) due to missing typedefs, presumably because the Clang used from the Nix sandbox doesn't set -D_DARWIN_C_SOURCE.

The content of interest is https://github.com/alexey-lysiuk/macos-sdk/blob/main/MacOSX26.1.sdk/usr/include/sys/types.h#L83-L96 which doesn't evaluate unless _DARWIN_C_SOURCE is set. The first POSIX branch is set because __STDC_ALLOC_LIB__ isn't: https://github.com/aws/aws-lc/blob/main/crypto/err/err.c#L113C8-L117

I suppose _POSIX_C_SOURCE was set for a reason and I can't figure out why a normal Cargo build would work - I cannot find any trace of __STDC_ALLOC_LIB__ - apart from a comment in #610.

The absence of _DARWIN_C_SOURCE causes the CC builder to throw:

In file included from /nix/var/nix/builds/nix-37298-3130532386/aws-lc-sys-0.32.3/aws-lc/crypto/fipsmodule/bcm.c:78:
In file included from /nix/var/nix/builds/nix-37298-3130532386/aws-lc-sys-0.32.3/aws-lc/crypto/fipsmodule/cpucap/cpu_aarch64_apple.c:20:
In file included from /nix/store/6py65dicilvc6qxfra4mzw0xpxw2vc06-apple-sdk-11.3/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/sysctl.h:83:
/nix/store/6py65dicilvc6qxfra4mzw0xpxw2vc06-apple-sdk-11.3/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/ucred.h:101:2:
error: unknown type name 'u_int'
  101 |         u_int   cr_version;             /* structure layout version */
      |         ^
In file included from /nix/var/nix/builds/nix-37298-3130532386/aws-lc-sys-0.32.3/aws-lc/crypto/fipsmodule/bcm.c:78:
In file included from /nix/var/nix/builds/nix-37298-3130532386/aws-lc-sys-0.32.3/aws-lc/crypto/fipsmodule/cpucap/cpu_aarch64_apple.c:20:
In file included from /nix/store/6py65dicilvc6qxfra4mzw0xpxw2vc06-apple-sdk-11.3/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/sysctl.h:85:
/nix/store/6py65dicilvc6qxfra4mzw0xpxw2vc06-apple-sdk-11.3/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/proc.h:116:2: error: unknown type name 'u_int'
  116 |         u_int   p_estcpu;        /* Time averaged value of p_cpticks. */
      |         ^
/nix/store/6py65dicilvc6qxfra4mzw0xpxw2vc06-apple-sdk-11.3/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/proc.h:121:2: error: unknown type name 'u_int'
  121 |         u_int   p_swtime;        /* Time swapped in or out. */
      |         ^
/nix/store/6py65dicilvc6qxfra4mzw0xpxw2vc06-apple-sdk-11.3/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/proc.h:122:2: error: unknown type name 'u_int'
  122 |         u_int   p_slptime;       /* Time since last blocked. */
      |         ^
/nix/store/6py65dicilvc6qxfra4mzw0xpxw2vc06-apple-sdk-11.3/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/proc.h:136:2: error: unknown type name 'u_char'; did you mean 'char'?
  136 |         u_char  p_priority;     /* Process priority. */
      |         ^
/nix/store/6py65dicilvc6qxfra4mzw0xpxw2vc06-apple-sdk-11.3/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/proc.h:137:2: error: unknown type name 'u_char'; did you mean 'char'?
  137 |         u_char  p_usrpri;       /* User-priority based on p_cpu and p_nice. */
      |         ^
/nix/store/6py65dicilvc6qxfra4mzw0xpxw2vc06-apple-sdk-11.3/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/proc.h:142:2: error: unknown type name 'u_short'; did you mean 'short'?
  142 |         u_short p_xstat;        /* Exit status for wait; also stop signal. */
      |         ^
/nix/store/6py65dicilvc6qxfra4mzw0xpxw2vc06-apple-sdk-11.3/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/proc.h:143:2: error: unknown type name 'u_short'; did you mean 'short'?
  143 |         u_short p_acflag;       /* Accounting flags. */
      |         ^

Call-outs:

This is unfamiliar territory for me. I don't know if configuring _POSIX_C_SOURCE appropriately is the better option.

Testing:

N/A

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.52%. Comparing base (c358484) to head (a85d004).
⚠️ Report is 288 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #941      +/-   ##
==========================================
- Coverage   95.80%   92.52%   -3.28%     
==========================================
  Files          61       74      +13     
  Lines        8143     9852    +1709     
  Branches        0     9852    +9852     
==========================================
+ Hits         7801     9116    +1315     
- Misses        342      449     +107     
- Partials        0      287     +287     

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[justsmth]

@martinjlowm -- Sorry, I've not had time to follow up with adding a test. I did push an update to this PR to conditionally set the define in a couple of places.

Can you confirm whether this latest change fixes the problem for you?