Fix clang build error in bitops.c (#1794)

In a recent PR #1741 the new
header `<immintrin.h>` was added, which transitively includes
`<mm_malloc.h>` header, where a function called `_mm_malloc(...)` makes
a call to the `malloc` function.

The Valkey server code explicitly sets the malloc function as a
deprecated function in `server.h`:
```c
void *malloc(size_t size) __attribute__((deprecated));
```

The Valkey server code is then compiled with
`-Werror=deprecated-declarations` option to detect the uses of
deprecated functions like `malloc`, and due to this, when the `bitops.c`
file is compiled with Clang, fails with the following error:

```
In file included from bitops.c:33:
In file included from /usr/lib/llvm-18/lib/clang/18/include/immintrin.h:26:
In file included from /usr/lib/llvm-18/lib/clang/18/include/xmmintrin.h:31:
/usr/lib/llvm-18/lib/clang/18/include/mm_malloc.h:35:12: error: 'malloc' is deprecated [-Werror,-Wdeprecated-declarations]
   35 |     return malloc(__size);
      |            ^
./server.h:3874:42: note: 'malloc' has been explicitly marked deprecated here
 3874 | void *malloc(size_t size) __attribute__((deprecated));
```

There is a difference in behavior though, between GCC and Clang. The
`bitops.c` file compiles successfully with GCC.

I don't know exactly why GCC does not issue a warning in this case. My
best guess is that GCC does not issue warnings from code of the standard
library.

To fix the build error in clang, we explicitly use `pragma` macro to
tell clang to ignore deprecated declarations warnings in `bitops.c`.

---------

Signed-off-by: Ricardo Dias <[email protected]>
Signed-off-by: Ricardo Dias <[email protected]>
Co-authored-by: Madelyn Olson <[email protected]>

Author: 2 people

src/bitops.c

@@ -30,6 +30,9 @@
 
 #include "server.h"
 #ifdef HAVE_AVX2
+/* Define __MM_MALLOC_H to prevent importing the memory aligned
+ * allocation functions, which we don't use. */
+#define __MM_MALLOC_H
 #include <immintrin.h>
 #endif
 /* -----------------------------------------------------------------------------