build: Fix Boost.Process test for Boost 1.78

configure.ac

@@ -1446,6 +1446,10 @@ 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"
@@ -1456,6 +1460,7 @@ if test "$use_external_signer" != "no"; then
         [have_boost_process="no"])
       LDFLAGS="$TEMP_LDFLAGS"
       CPPFLAGS="$TEMP_CPPFLAGS"
+      CXXFLAGS="$TEMP_CXXFLAGS"
       AC_MSG_RESULT([$have_boost_process])
       if test "$have_boost_process" = "yes"; then
         use_external_signer="yes"

src/test/system_tests.cpp

@@ -12,7 +12,16 @@
 // For details see https://github.com/bitcoin/bitcoin/pull/22348.
 #define __kernel_entry
 #endif
+#if defined(__GNUC__)
+// Boost 1.78 requires the following workaround.
+// See: https://github.com/boostorg/process/issues/235
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wnarrowing"
+#endif
 #include <boost/process.hpp>
+#if defined(__GNUC__)
+#pragma GCC diagnostic pop
+#endif
 #endif // ENABLE_EXTERNAL_SIGNER
 
 #include <boost/test/unit_test.hpp>

src/util/system.cpp

@@ -6,7 +6,16 @@
 #include <util/system.h>
 
 #ifdef ENABLE_EXTERNAL_SIGNER
+#if defined(__GNUC__)
+// Boost 1.78 requires the following workaround.
+// See: https://github.com/boostorg/process/issues/235
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wnarrowing"
+#endif
 #include <boost/process.hpp>
+#if defined(__GNUC__)
+#pragma GCC diagnostic pop
+#endif
 #endif // ENABLE_EXTERNAL_SIGNER
 
 #include <chainparamsbase.h>