capnproto: add patch to fix powerpc-linux build

From dfbbc505817bd0c3e01af5865196629c2a2a2b5e Mon Sep 17 00:00:00 2001

From: Marie Ramlow <me@nycode.dev>

Date: Wed, 10 Sep 2025 20:12:39 +0200

Subject: [PATCH] Check if libatomic is needed

---

 c++/src/kj/CMakeLists.txt | 15 +++++++++++++++

 1 file changed, 15 insertions(+)

diff --git a/c++/src/kj/CMakeLists.txt b/c++/src/kj/CMakeLists.txt

index 7114ddb80e..8ce355b8b0 100644

--- a/c++/src/kj/CMakeLists.txt

+++ b/c++/src/kj/CMakeLists.txt

@@ -84,6 +84,21 @@ target_compile_features(kj PUBLIC cxx_std_20)

 if(UNIX AND NOT ANDROID)

   target_link_libraries(kj PUBLIC pthread)

 endif()

+

+include(CheckCXXSourceCompiles)

+check_cxx_source_compiles("#include <atomic>

+int main() {

+  std::atomic<uint8_t> w1;

+  std::atomic<uint16_t> w2;

+  std::atomic<uint32_t> w4;

+  std::atomic<uint64_t> w8;

+  return ++w1 + ++w2 + ++w4 + ++w8;

+}" CAPNP_BUILDS_WITHOUT_LIBATOMIC)

+

+if(NOT CAPNP_BUILDS_WITHOUT_LIBATOMIC)

+  target_link_libraries(kj PUBLIC atomic)

+endif()

+

 #make sure the lite flag propagates to all users (internal + external) of this library

 target_compile_definitions(kj PUBLIC ${CAPNP_LITE_FLAG})

 #make sure external consumers don't need to manually set the include dirs

  patches = [

    # https://github.com/capnproto/capnproto/pull/2377

    ./fix-libucontext.patch

    # https://github.com/capnproto/capnproto/pull/2410

    ./fix-libatomic.patch

  ];

  nativeBuildInputs = [