Merge branch 'develop'

Fix for numeric overflow found during fuzzing.

.github/workflows/ci.yml

@@ -158,7 +158,7 @@ jobs:
         run: ../../../b2 toolset=${{ matrix.toolset }} cxxstd=${{ matrix.standard }}
         working-directory: ../boost-root/libs/regex/test
   windows_gcc:
-    runs-on: windows-latest
+    runs-on: windows-2019
     defaults:
       run:
         shell: cmd

include/boost/regex/v5/basic_regex_creator.hpp

@@ -1019,6 +1019,8 @@ int basic_regex_creator<charT, traits>::calculate_backstep(re_syntax_base* state
             {
                if(rep->max != rep->min)
                   return -1;
+               if (static_cast<std::size_t>((std::numeric_limits<int>::max)() - result) < rep->min)
+                  return -1; // protection against overflow, we can't calculate a backstep in this case and the expression is probably ill-formed.
                result += static_cast<int>(rep->min);
                state = rep->alt.p;
                continue;