build: disable external signer on Windows

ci/test/00_setup_env_win64.sh

@@ -13,4 +13,4 @@ export DPKG_ADD_ARCH="i386"
 export PACKAGES="python3 nsis g++-mingw-w64-x86-64 wine-binfmt wine64 wine32 file"
 export RUN_FUNCTIONAL_TESTS=false
 export GOAL="deploy"
-export BITCOIN_CONFIG="--enable-reduce-exports --disable-gui-tests --disable-external-signer"
+export BITCOIN_CONFIG="--enable-reduce-exports --disable-gui-tests"

configure.ac

@@ -321,7 +321,7 @@ AC_ARG_ENABLE([werror],
 AC_ARG_ENABLE([external-signer],
     [AS_HELP_STRING([--enable-external-signer],[compile external signer support (default is yes, requires Boost::Process)])],
     [use_external_signer=$enableval],
-    [use_external_signer=yes])
+    [use_external_signer=auto])
 
 AC_ARG_ENABLE([lto],
     [AS_HELP_STRING([--enable-lto],[build using LTO (default is no)])],
@@ -1415,7 +1415,21 @@ if test "$use_boost" = "yes"; then
 fi
 
 if test "$use_external_signer" != "no"; then
-  AC_DEFINE([ENABLE_EXTERNAL_SIGNER], [], [Define if external signer support is enabled])
+  case $host in
+    *mingw*)
+      dnl Boost Process uses Boost Filesystem when targeting Windows. Also,
+      dnl since Boost 1.71.0, Process does not work with mingw-w64 without
+      dnl workarounds. See 67669ab425b52a2b6be3d2f3b3b7e3939b676a2c.
+      if test "$use_external_signer" = "yes"; then
+        AC_MSG_ERROR([External signing is not supported on Windows])
+      fi
+      use_external_signer="no";
+    ;;
+    *)
+      use_external_signer="yes"
+      AC_DEFINE([ENABLE_EXTERNAL_SIGNER], [1], [Define if external signer support is enabled])
+    ;;
+  esac
 fi
 AM_CONDITIONAL([ENABLE_EXTERNAL_SIGNER], [test "$use_external_signer" = "yes"])
 

src/util/system.cpp

@@ -6,11 +6,6 @@
 #include <util/system.h>
 
 #ifdef ENABLE_EXTERNAL_SIGNER
-#if defined(WIN32) && !defined(__kernel_entry)
-// A workaround for boost 1.71 incompatibility with mingw-w64 compiler.
-// For details see https://github.com/bitcoin/bitcoin/pull/22348.
-#define __kernel_entry
-#endif
 #include <boost/process.hpp>
 #endif // ENABLE_EXTERNAL_SIGNER