[libcxx] [llvm] [libc++] Fix `regex_search` to match `$` alone with `match_default` flag (PR #77256)

[Sanjay Marreddi via llvm-commits]

================
@@ -47,5 +47,12 @@ int main(int, char**)
     assert( std::regex_search(target, re, std::regex_constants::match_not_eol));
     }
 
+    {
+      std::string target = "foo";
+      std::regex re("$");
+      assert(std::regex_search(target, re));
+      assert(!std::regex_search(target, re, std::regex_constants::match_not_eol));
----------------
SanjayMarreddi wrote:

Done

https://github.com/llvm/llvm-project/pull/77256