std.zig: handle -frandom-seed in NIX_CFLAGS_COMPILE

[sagehane]

Closes #8269 by ignoring the value of the -frandom-seed flag.

It would be nice to have it addressed before the upcoming NixOS release (21.05).

[LemonBoy]

I think a better and more future-proof solution would be to make the unrecognized flag error a non-fatal one.

[sagehane]

I guess simply removing the break from the unrecognized flag case would work. This makes sure the compiler keeps going after coming across an unrecognized flag, as opposed to just aborting.

diff --git a/lib/std/zig/system.zig b/lib/std/zig/system.zig
index 42099c6ef..85b5da38e 100644
--- a/lib/std/zig/system.zig
+++ b/lib/std/zig/system.zig
@@ -54,7 +54,6 @@ pub const NativePaths = struct {
                     try self.addIncludeDir(include_path);
                 } else {
                     try self.addWarningFmt("Unrecognized C flag from NIX_CFLAGS_COMPILE: {s}", .{word});
-                    break;
                 }
             }
         } else |err| switch (err) {

However, that would cause it to always leave a message like this:

$ ../zig/build/bin/zig build
warning: Unrecognized C flag from NIX_CFLAGS_COMPILE: -frandom-seed=yymb0qgbfh

I'm fine with this as long as getting that warn message every time isn't deemed too annoying. Or, both methods can be applied so -frandom-seed is properly dealt with, and any new C flag NixOS introduces won't be fatal.

[andrewrk]

Thanks @sagehane!