message: build: don't try and use -fstack-clash-protection on Windows
  This has never worked with any of the mingw-w64 compilers we use, and
  the -O0 is causing issues for builders applying spectre mitigations.
  Recent discussion on
  also indicates that this should just not be used on Windows.
diff: @@ -868,11 +868,16 @@ if test x$use_hardening != xno; then
  dnl Use CHECK_LINK_FLAG & --fatal-warnings to ensure we won't use the flag in this case.
  AX_CHECK_LINK_FLAG([-fcf-protection=full],[HARDENED_CXXFLAGS="$HARDENED_CXXFLAGS -fcf-protection=full"],, [[$LDFLAG_WERROR]])
  - dnl stack-clash-protection does not work properly when building for Windows.
  - dnl We use the test case from https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90458
  - dnl to determine if it can be enabled.
  - AX_CHECK_COMPILE_FLAG([-fstack-clash-protection],[HARDENED_CXXFLAGS="$HARDENED_CXXFLAGS -fstack-clash-protection"],[],["-O0"],
  - [AC_LANG_SOURCE([[class D {public: unsigned char buf[32768];}; int main() {D d; return 0;}]])])
  + case $host in
  + *mingw*)
  + dnl stack-clash-protection doesn't currently work, and likely should just be skipped for Windows.
  + dnl See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90458 for more details.
  + ;;
  + *)
  + AX_CHECK_COMPILE_FLAG([-fstack-clash-protection],[HARDENED_CXXFLAGS="$HARDENED_CXXFLAGS -fstack-clash-protection"])
  + ;;
  + esac
  +
  dnl When enable_debug is yes, all optimizations are disabled.
  dnl However, FORTIFY_SOURCE requires that there is some level of optimization, otherwise it does nothing and just creates a compiler warning.
  