Merge bitcoin#28084: doc: update windows -fstack-clash-protection doc

05ef059 doc: update windows -fstack-clash-protection doc (fanquake)

Pull request description:

  Now that changes have been made in GCC, to fix the build failures.
  See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90458.

ACKs for top commit:
  TheCharlatan:
    ACK 05ef059
  hebasto:
    ACK 05ef059, I've verified that the fix commit is present in all branches starting from `gcc-11`.

Tree-SHA512: 96b79d65b46e6b9d939c8e6079e984da86987503210106d5155dbe5a6fd82d56d9983694656e27156b01bab795c766b85fc60c799813bc676bba5f3b73f9be22

configure.ac

@@ -955,7 +955,8 @@ if test x$use_hardening != xno; then
 
   case $host in
     *mingw*)
-      dnl stack-clash-protection doesn't currently work, and likely should just be skipped for Windows.
+      dnl stack-clash-protection doesn't compile with GCC 10 and earlier.
+      dnl In any case, it is a no-op for Windows.
       dnl See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90458 for more details.
       ;;
     *)