merge bitcoin#28092: document that -Wreturn-type has been fixed upstream (mingw-w64)

Author: kwvg

ci/test/00_setup_env_win64.sh

@@ -13,5 +13,8 @@ export PACKAGES="python3 nsis g++-mingw-w64-x86-64-posix wine-binfmt wine64 wine
 export RUN_FUNCTIONAL_TESTS=false
 export RUN_SECURITY_TESTS="false"
 export GOAL="deploy"
-export BITCOIN_CONFIG="--enable-gui --enable-reduce-exports --disable-miner --without-boost-process"
+# Prior to 11.0.0, the mingw-w64 headers were missing noreturn attributes, causing warnings when
+# cross-compiling for Windows. https://sourceforge.net/p/mingw-w64/bugs/306/
+# https://github.com/mingw-w64/mingw-w64/commit/1690994f515910a31b9fb7c7bd3a52d4ba987abe
+export BITCOIN_CONFIG="--enable-gui --enable-reduce-exports --disable-miner --without-boost-process CXXFLAGS=-Wno-return-type"
 export DIRECT_WINE_EXEC_TESTS=true

configure.ac

@@ -452,12 +452,6 @@ if test "$enable_werror" = "yes"; then
   fi
   ERROR_CXXFLAGS=$CXXFLAG_WERROR
 
-  dnl -Wreturn-type is broken in GCC for MinGW-w64.
-  dnl https://sourceforge.net/p/mingw-w64/bugs/306/
-  AX_CHECK_COMPILE_FLAG([-Werror=return-type], [], [ERROR_CXXFLAGS="$ERROR_CXXFLAGS -Wno-error=return-type"], [$CXXFLAG_WERROR],
-                        [AC_LANG_SOURCE([[#include <cassert>
-                                          int f(){ assert(false); }]])])
-
   dnl -Wstringop-overread and -Wstringop-overflow are broken in gcc
   AX_CHECK_COMPILE_FLAG([-Wstringop-overread], [WARN_CXXFLAGS="$WARN_CXXFLAGS -Wno-stringop-overread"], [], [$CXXFLAG_WERROR])
   AX_CHECK_COMPILE_FLAG([-Wstringop-overflow], [WARN_CXXFLAGS="$WARN_CXXFLAGS -Wno-stringop-overflow"], [], [$CXXFLAG_WERROR])