cmake, ci: updates for recent nixpkgs

[ryanofsky]

This PR fixes two problems that happen with recent nixpkgs. The first commit works around compilation errors that happen when IWYU is enabled with (-DMP_ENABLE_IWYU=ON) that were caused by NixOS/nixpkgs#445095. The second commit fixes problems building old versions of Cap'n Proto with CMake 4.0 in shell.nix.

Neither problem has showed up so far running in github actions, only running locally with unstable nixpkgs. More details about the problems and fixes are in the commit messages.

[DrahtBot]

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Type	Reviewers
ACK	sedited, hebasto

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Conflicts

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• #276 (build: prepare for subtree split by Sjors)

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[hebasto]

ACK b66a6d3, I have reviewed the code and it looks OK.

[ryanofsky]

Updated b66a6d3 -> db7acb3 (pr/iwyufu.2 -> pr/iwyufu.3, compare) to remove an incorrect comment in the b66a6d3 commit message about the cmake 4.0 problem not affecting the olddeps CI job. The problem does affect the olddeps job when I run it locally. It doesn't affect github actions CI just because it is currently using CMake 3.31.6.

[sedited]

ACK db7acb3

[hebasto]

re-ACK db7acb3.

[ryanofsky]

In commit "cmake: Fix IWYU in nix by adding CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES" (91a7759)

Note: I might merge this PR anyway since it has two acks, but this comment isn't exactly right since newer versions of clang-tidy in nixpkgs fix the issue and make this workaround unnecessary. The fix was NixOS/nixpkgs@d46fa26 (NixOS/nixpkgs#462747).

The problem with IWYU still exists but can be fixed with a similar change, which should probably be a PR:

--- a/pkgs/development/tools/analysis/include-what-you-use/wrapper
+++ b/pkgs/development/tools/analysis/include-what-you-use/wrapper
@@ -4,7 +4,7 @@ buildcpath() {
   local path after
   while (( $# )); do
     case $1 in
-        -isystem)
+        -isystem|-cxx-isystem)
             shift
             path=$path${path:+':'}$1
             ;;