Steps to reproduce

1. Setup symlinks for the custom toolchain

   cd engine/src/flutter/buildtools/linux-x64/clang/bin
   ln -s llvm-ar armv7-unknown-linux-gnueabihf-ar
   ln -s llvm-readelf armv7-unknown-linux-gnueabihf-readelf
   ln -s llvm-nm armv7-unknown-linux-gnueabihf-nm
   ln -s llvm-strip armv7-unknown-linux-gnueabihf-strip
   

2. From a Linux host, cross compile to a Linux target with --enable-minimal-linux

   ./engine/src/flutter/tools/gn \
       --target-os=linux \
       --linux-cpu=arm \
       --enable-minimal-linux \
       --arm-float-abi=hard \
       --disable-desktop-embeddings \
       --embedder-for-target \
       --target-triple=armv7-unknown-linux-gnueabihf \
       --target-sysroot= # some sysroot without X11 libraries \
       --target-toolchain=$(pwd)/engine/src/flutter/buildtools/linux-x64/clang
   ninja -C engine/src/out/linux_debug_unopt_arm flutter/shell/platform/embedder:flutter_engine
   

Expected results

The build completes successfully

Actual results

A build error occurs from the vulkan headers

../../flutter/third_party/vulkan-deps/vulkan-headers/src/include/vulkan/vulkan.h:52:10: fatal error: 'xcb/xcb.h' file not found
   52 | #include <xcb/xcb.h>
      |          ^~~~~~~~~~~
1 error generated.