Redis [BUG] Redis fails to compile if HAVE_MALLOC_SIZE is not defined

Describe the bug

Compiling Redis 6.2.0 on a system without malloc_usable_size() or similar with USE_JEMALLOC=No results in a build failure. The following is seen on OpenBSD -current (amd64 with clang 10.0.1):

zmalloc.c:60:5: error: function-like macro 'sizeof' is not defined
#if PREFIX_SIZE > 0
    ^
zmalloc.c:56:22: note: expanded from macro 'PREFIX_SIZE'
#define PREFIX_SIZE (sizeof(size_t))
                     ^
1 error generated.

https://github.com/redis/redis/blob/8e83bcd2acb18370e2d6cea3718339792322e80f/src/zmalloc.c#L60-L64

The issue is that at the preprocessing stage keywords like sizeof do not exist (see C11 6.10, footnote 166), so if HAVE_MALLOC_SIZE is not defined, the above conditional won't be accepted by either clang or gcc.

https://github.com/redis/redis/blob/8e83bcd2acb18370e2d6cea3718339792322e80f/src/zmalloc.c#L50-L58

To reproduce

Compile Redis 6.2.0 on a system without malloc_usable_size() or similar with USE_JEMALLOC=No.

Expected behavior

Redis compiles

Additional information

I think the following diff would make sense, which I can submit as a PR if that's acceptable. I expect all versions having a version of https://github.com/redis/redis/pull/8522 to be affected.

--- src/zmalloc.c.orig
+++ src/zmalloc.c
@@ -28,6 +28,7 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */

+#include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>
@@ -57,7 +58,7 @@ void zlibc_free(void *ptr) {
 #endif
 #endif

-#if PREFIX_SIZE > 0
+#ifndef HAVE_MALLOC_SIZE
 #define ASSERT_NO_SIZE_OVERFLOW(sz) assert((sz) + PREFIX_SIZE > (sz))
 #else
 #define ASSERT_NO_SIZE_OVERFLOW(sz)