fix: replace free() with std::free() (#3321)

* Disambiguate free() to use std::free()

* Add cstdlib include

include/pybind11/pybind11.h

@@ -16,6 +16,7 @@
 #include "detail/class.h"
 #include "detail/init.h"
 
+#include <cstdlib>
 #include <memory>
 #include <new>
 #include <vector>
@@ -1536,7 +1537,7 @@ public:
            char *doc_prev = rec_fget->doc; /* 'extra' field may include a property-specific documentation string */
            detail::process_attributes<Extra...>::init(extra..., rec_fget);
            if (rec_fget->doc && rec_fget->doc != doc_prev) {
-              free(doc_prev);
+              std::free(doc_prev);
               rec_fget->doc = PYBIND11_COMPAT_STRDUP(rec_fget->doc);
            }
         }
@@ -1544,7 +1545,7 @@ public:
             char *doc_prev = rec_fset->doc;
             detail::process_attributes<Extra...>::init(extra..., rec_fset);
             if (rec_fset->doc && rec_fset->doc != doc_prev) {
-                free(doc_prev);
+                std::free(doc_prev);
                 rec_fset->doc = PYBIND11_COMPAT_STRDUP(rec_fset->doc);
             }
             if (! rec_active) rec_active = rec_fset;

tests/test_embed/test_interpreter.cpp

@@ -8,6 +8,7 @@
 
 #include <catch.hpp>
 
+#include <cstdlib>
 #include <fstream>
 #include <functional>
 #include <thread>
@@ -315,7 +316,7 @@ TEST_CASE("sys.argv gets initialized properly") {
     {
         char *argv[] = {strdup("a.out")};
         py::scoped_interpreter argv_scope(true, 1, argv);
-        free(argv[0]);
+        std::free(argv[0]);
         auto module = py::module::import("test_interpreter");
         auto py_widget = module.attr("DerivedWidget")("The question");
         const auto &cpp_widget = py_widget.cast<const Widget &>();