build: remove boost::process dependency for building external signer support

configure.ac

@@ -307,9 +307,9 @@ AC_ARG_ENABLE([werror],
     [enable_werror=no])
 
 AC_ARG_ENABLE([external-signer],
-    [AS_HELP_STRING([--enable-external-signer],[compile external signer support (default is auto, requires Boost::Process)])],
+    [AS_HELP_STRING([--enable-external-signer],[compile external signer support (default is yes)])],
     [use_external_signer=$enableval],
-    [use_external_signer=auto])
+    [use_external_signer=yes])
 
 AC_LANG_PUSH([C++])
 
@@ -1439,56 +1439,14 @@ if test "$use_boost" = "yes"; then
   fi
 fi
 
-if test "$use_external_signer" != "no"; then
-  AC_MSG_CHECKING([whether Boost.Process can be used])
-  TEMP_CXXFLAGS="$CXXFLAGS"
-  dnl Boost 1.78 requires the following workaround.
-  dnl See: https://github.com/boostorg/process/issues/235
-  CXXFLAGS="$CXXFLAGS -Wno-error=narrowing"
-  TEMP_CPPFLAGS="$CPPFLAGS"
-  CPPFLAGS="$CPPFLAGS $BOOST_CPPFLAGS"
-  TEMP_LDFLAGS="$LDFLAGS"
-  dnl Boost 1.73 and older require the following workaround.
-  LDFLAGS="$LDFLAGS $PTHREAD_CFLAGS"
-  AC_LINK_IFELSE([AC_LANG_PROGRAM([[
-    #define BOOST_PROCESS_USE_STD_FS
-    #include <boost/process.hpp>
-  ]],[[
-    namespace bp = boost::process;
-    bp::opstream stdin_stream;
-    bp::ipstream stdout_stream;
-    bp::child c("dummy", bp::std_out > stdout_stream, bp::std_err > stdout_stream, bp::std_in < stdin_stream);
-    stdin_stream << std::string{"test"} << std::endl;
-    if (c.running()) c.terminate();
-    c.wait();
-    c.exit_code();
-  ]])],
-    [have_boost_process="yes"],
-    [have_boost_process="no"])
-  LDFLAGS="$TEMP_LDFLAGS"
-  CPPFLAGS="$TEMP_CPPFLAGS"
-  CXXFLAGS="$TEMP_CXXFLAGS"
-  AC_MSG_RESULT([$have_boost_process])
-  if test "$have_boost_process" = "yes"; then
-    case $host in
-      dnl Boost Process for Windows uses Boost ASIO. Boost ASIO performs
-      dnl pre-main init of Windows networking libraries, which we do not
-      dnl want.
-      *mingw*)
-        use_external_signer="no"
-      ;;
-      *)
-        use_external_signer="yes"
-        AC_DEFINE([ENABLE_EXTERNAL_SIGNER], [1], [Define if external signer support is enabled])
-        AC_DEFINE([BOOST_PROCESS_USE_STD_FS], [1], [Defined to avoid Boost::Process trying to use Boost Filesystem])
-      ;;
-    esac
-  else
-    if test "$use_external_signer" = "yes"; then
-      AC_MSG_ERROR([External signing is not supported for this Boost version])
-    fi
-    use_external_signer="no";
-  fi
+case $host in
+  dnl Re-enable it after enabling Windows support in cpp-subprocess.
+  *mingw*)
+    use_external_signer="no"
+  ;;
+esac
+if test "$use_external_signer" = "yes"; then
+  AC_DEFINE([ENABLE_EXTERNAL_SIGNER], [1], [Define if external signer support is enabled])
 fi
 AM_CONDITIONAL([ENABLE_EXTERNAL_SIGNER], [test "$use_external_signer" = "yes"])