fix raw_ptr.cc on exotic architectures (#18193)

I was working with an exotic architecture where ABSL_CACHELINE_SIZE of abseil was less than 64, so I got a compilation error about redefined symbols. I think the cc file should be adapted to the header file, so here is my change.

Closes #18193

COPYBARA_INTEGRATE_REVIEW=#18193 from jagub2:raw_ptr_fix 4958e0f
FUTURE_COPYBARA_INTEGRATE_REVIEW=#18193 from jagub2:raw_ptr_fix 4958e0f
PiperOrigin-RevId: 676526640

src/google/protobuf/raw_ptr.cc

@@ -7,6 +7,8 @@
 
 #include "google/protobuf/raw_ptr.h"
 
+#include <algorithm>
+
 #include "absl/base/attributes.h"
 #include "absl/base/optimization.h"
 
@@ -17,8 +19,8 @@ namespace google {
 namespace protobuf {
 namespace internal {
 
-ABSL_CONST_INIT PROTOBUF_EXPORT
-    ABSL_CACHELINE_ALIGNED const char kZeroBuffer[ABSL_CACHELINE_SIZE] = {};
+ABSL_CONST_INIT PROTOBUF_EXPORT ABSL_CACHELINE_ALIGNED const char
+    kZeroBuffer[std::max(ABSL_CACHELINE_SIZE, 64)] = {};
 
 }  // namespace internal
 }  // namespace protobuf