Fix Bitcoin Core build errors from libmultiprocess headers

ci/configs/default.bash

@@ -1,5 +1,5 @@
 CI_DESC="CI job using default libraries and tools, and running IWYU"
 CI_DIR=build-default
-export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wno-unused-parameter -Wextra-semi -Wmissing-noreturn -Wtrailing-whitespace"
+export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wundef -Wunused-const-variable -Wno-unused-parameter -Wextra-semi -Wmissing-noreturn -Wtrailing-whitespace"
 CMAKE_ARGS=(-DMP_ENABLE_IWYU=ON)
 BUILD_ARGS=(-k)

ci/configs/gnu32.bash

@@ -6,6 +6,6 @@ NIX_ARGS=(
   --arg minimal true
   --arg crossPkgs 'import <nixpkgs> { crossSystem = { config = "i686-unknown-linux-gnu"; }; }'
 )
-export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wno-unused-parameter"
+export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wunused-const-variable -Wno-unused-parameter"
 CMAKE_ARGS=(-G Ninja)
 BUILD_ARGS=(-k 0)

ci/configs/llvm.bash

@@ -2,7 +2,7 @@ CI_DESC="CI job using LLVM-based libraries and tools (clang, libc++, clang-tidy,
 CI_DIR=build-llvm
 NIX_ARGS=(--arg enableLibcxx true)
 export CXX=clang++
-export CXXFLAGS="-Werror -Wall -Wextra -Wextra-semi -Wpedantic -Wthread-safety -Wno-unused-parameter -Wno-c++23-lambda-attributes"
+export CXXFLAGS="-Werror -Wall -Wextra -Wextra-semi -Wpedantic -Wundef -Wthread-safety -Wno-unused-parameter -Wno-c++23-lambda-attributes"
 CMAKE_ARGS=(
   -G Ninja
   -DMP_ENABLE_CLANG_TIDY=ON

ci/configs/newdeps.bash

@@ -1,6 +1,6 @@
 CI_DESC="CI job using newest Cap'n Proto and cmake versions"
 CI_DIR=build-newdeps
-export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wno-unused-parameter -Wno-error=array-bounds"
+export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wunused-const-variable -Wno-unused-parameter -Wno-error=array-bounds"
 CAPNP_CHECKOUT=master  # This is the v1.x release branch
 NIX_ARGS=(--argstr capnprotoVersion "none" --argstr cmakeVersion "4.3.4")
 BUILD_ARGS=(-k)

ci/configs/olddeps.bash

@@ -2,7 +2,7 @@ CI_DESC="CI job using old Cap'n Proto and cmake versions"
 CI_DIR=build-olddeps
 # Pin olddeps to an older Nixpkgs channel, to be able to test an older GCC.
 CI_NIXPKGS_CHANNEL=nixos-25.05
-export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wno-unused-parameter -Wno-error=array-bounds"
+export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wunused-const-variable -Wno-unused-parameter -Wno-error=array-bounds"
 CAPNP_CHECKOUT=v0.9.2  # Use a checkout to compile it with the selected GCC
 NIX_ARGS=(--argstr capnprotoVersion "none" --argstr cmakeVersion "3.12.4" --argstr gccVersion "10")
 BUILD_ARGS=(-k)

include/mp/proxy-types.h

@@ -15,7 +15,7 @@
 
 // KJ exception support is required, or exceptions thrown in serverInvoke below go uncaught
 // and crash the process instead of being returned to the client as errors.
-#if KJ_NO_EXCEPTIONS
+#if defined(KJ_NO_EXCEPTIONS) && KJ_NO_EXCEPTIONS
 #error "KJ_NO_EXCEPTIONS=1 is set but libmultiprocess requires support for exceptions. Please check build settings. On NetBSD you may also need to set -DKJ_NO_EXCEPTIONS=0 -DKJ_NO_RTTI=0 explicitly (https://github.com/capnproto/capnproto/pull/2756)"
 #endif
 

include/mp/util.h

@@ -293,7 +293,7 @@ using Stream = kj::Own<kj::AsyncIoStream>;
 
 using ProcessId = int;
 using SocketId = int;
-constexpr SocketId SocketError{-1};
+inline constexpr SocketId SocketError{-1};
 
 //! Information about parent process passed to child process as a command-line
 //! argument. On unix this is the child socket fd number formatted as a string.