meta: fix 'zig build -Denable-llvm' on nixos 24

[nektro]

No description provided.

[alexrp]

This entire code path looks insanely sus to my non-NixOS-using sensibilities but I guess one more flag isn't going to be the end of the world.

[Jan200101]

I'm not entirely sure what this is suppose to do.
Zig already ignores any C flags it doesn't recognize, what does this change which fixes building on nixos?

[nektro]

it prevents this

[nix-shell:~/src/zig/build]$ ./stage3/bin/zig build -p ./stage4 -Doptimize=ReleaseSafe -Denable-llvm
install
└─ install zig
   └─ zig build-exe zig ReleaseSafe native failure
error: warning: Unrecognized C flag from NIX_CFLAGS_COMPILE: -idirafter
warning: Unrecognized C flag from NIX_CFLAGS_COMPILE: /usr/include

upon further inspection it does appear a binary may still have been produced

[nix-shell:~/src/zig/build]$ ll ./stage4/bin/zig 
-rwxr-xr-x 1 meghan users 138913688 Feb  5 02:08 ./stage4/bin/zig

[nix-shell:~/src/zig/build]$ ./stage4/bin/zig version
0.14.0-dev.3051+cf059ee08

[erikarvstedt]

In Nix build environments on Linux, -idirafter in NIX_CFLAGS_COMPILE is usually not set by the stdenv or any pkgs.
But it might be set by default on Darwin (see this nixpkgs sourcegraph search).
@nektro, are you on Darwin?

In any case, -idirafter shouldn't be silently ignored, because a user might have intentionally added this flag.

[nektro]

no im on nixos 24.05 linux

[erikarvstedt]

Related: #18998

[nektro]

its odd because if i echo $NIX_CFLAGS_COMPILE inside my zig dev environment i get this and no sign of -idirafter

-frandom-seed=zpc3qrs0li
-isystem /nix/store/zps3l0mc26r7bvjqd8x0y1lbc6gmbdvn-gnumake-4.4.1/include
-isystem /nix/store/06q0p7bhn2ffxxya20rrfqdib3h32csn-zlib-1.3.1-dev/include
-isystem /nix/store/q474makx3105m1493i8fg8al1pf8z18p-libxml2-2.13.5-dev/include
-isystem /nix/store/9i7q9wy845i5na9bccpdial1va49gsr9-llvm-19.1.7-dev/include
-isystem /nix/store/69v6c64pn1ay26207b0cmzi40qpr9q0w-ncurses-6.4.20221231-dev/include
-isystem /nix/store/zj8ywgyz8nnhq995q798r5hhqlndbars-lld-19.1.7-dev/include
-isystem /nix/store/6fmmfc0fa3wzyb02nmsx6qd73cmka91f-clang-19.1.7-dev/include
-isystem /nix/store/zps3l0mc26r7bvjqd8x0y1lbc6gmbdvn-gnumake-4.4.1/include
-isystem /nix/store/06q0p7bhn2ffxxya20rrfqdib3h32csn-zlib-1.3.1-dev/include
-isystem /nix/store/q474makx3105m1493i8fg8al1pf8z18p-libxml2-2.13.5-dev/include
-isystem /nix/store/9i7q9wy845i5na9bccpdial1va49gsr9-llvm-19.1.7-dev/include
-isystem /nix/store/69v6c64pn1ay26207b0cmzi40qpr9q0w-ncurses-6.4.20221231-dev/include
-isystem /nix/store/zj8ywgyz8nnhq995q798r5hhqlndbars-lld-19.1.7-dev/include
-isystem /nix/store/6fmmfc0fa3wzyb02nmsx6qd73cmka91f-clang-19.1.7-dev/include

[andrewrk]

? will incorrectly crash if missing arg. also the information must not be discarded.