build.zig: don't completely fail if git describe --tags fails

But also, inherit stderr so we can actually see why.

Author: mlugg

build.zig

@@ -287,13 +287,11 @@ fn generateHeaders(b: *std.Build) std.Build.LazyPath {
     const version: []const u8 = b.runAllowFail(
         &.{ "git", "describe", "--tags" },
         &git_exit,
-        .Ignore,
-    ) catch |err| switch (err) {
-        error.InvalidExe => version: {
-            std.log.warn("git not found; leaving version blank", .{});
-            break :version "";
-        },
-        else => std.debug.panic("failed to spawn git: {s}", .{@errorName(err)}),
+        .Inherit,
+    ) catch |err| v: {
+        std.log.warn("failed to run git: {s}", .{@errorName(err)});
+        std.log.warn("using blank version string", .{});
+        break :v "";
     };
     const is_canary = b.option(bool, "canary", "Whether this is a canary build of SAR; default true") orelse true;
     const demo_sign_pubkey = b.option([]const u8, "demo-sign-pubkey", "The public key to use for demo signing.") orelse "";