Resolve gcc 4.8.5 error:

```
pytypes.h:1615:12: error: missing space between '""' and suffix identifier
```

include/pybind11/cast.h

@@ -1377,7 +1377,15 @@ inline namespace literals {
 /** \rst
     String literal version of `arg`
  \endrst */
-constexpr arg operator""_a(const char *name, size_t) { return arg(name); }
+constexpr arg
+#if defined(__GNUC__) && __GNUC__ < 5
+operator"" _a // gcc 4.8.5 insists on having a space (hard error).
+#else
+operator""_a // clang 17 generates a deprecation warning if there is a space.
+#endif
+    (const char *name, size_t) {
+    return arg(name);
+}
 } // namespace literals
 
 PYBIND11_NAMESPACE_BEGIN(detail)

include/pybind11/pytypes.h

@@ -1612,7 +1612,15 @@ inline namespace literals {
 /** \rst
     String literal version of `str`
  \endrst */
-inline str operator""_s(const char *s, size_t size) { return {s, size}; }
+inline str
+#if defined(__GNUC__) && __GNUC__ < 5
+operator"" _s // gcc 4.8.5 insists on having a space (hard error).
+#else
+operator""_s // clang 17 generates a deprecation warning if there is a space.
+#endif
+    (const char *s, size_t size) {
+    return {s, size};
+}
 } // namespace literals
 
 /// \addtogroup pytypes