Don't include config.h from serverassert.h (#404)

Serverassert is a drop-in replacement of assert. We use it even in code
copied from other sources. To make these files usable outside of Valkey,
it should be enough to replace the `serverassert.h` include with
`<assert.h>`. Therefore, this file shouldn't have any dependencies to
the rest of the valkey code.

---------

Signed-off-by: Viktor Söderqvist <viktor.soderqvist@est.tech>

src/serverassert.h

@@ -38,7 +38,20 @@
 #ifndef VALKEY_ASSERT_H
 #define VALKEY_ASSERT_H
 
-#include "config.h"
+/* This file shouldn't have any dependencies to any other Valkey code. */
+
+#if __GNUC__ >= 5 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5)
+#define valkey_unreachable __builtin_unreachable
+#else
+#include <stdlib.h>
+#define valkey_unreachable abort
+#endif
+
+#if __GNUC__ >= 3
+#define likely(x) __builtin_expect(!!(x), 1)
+#else
+#define likely(x) (x)
+#endif
 
 #define assert(_e) (likely((_e))?(void)0 : (_serverAssert(#_e,__FILE__,__LINE__),valkey_unreachable()))
 #define panic(...) _serverPanic(__FILE__,__LINE__,__VA_ARGS__),valkey_unreachable()