Allow to disable ZEND_HIGH_HALF_KERNEL

Author: arnaud-lb

Zend/zend_portability.h

@@ -873,8 +873,9 @@ static zend_always_inline uint64_t ZEND_BYTES_SWAP64(uint64_t u)
 # define UINTPTR_WIDTH (CHAR_BITS * sizeof(uintptr_t))
 #endif
 
-#if (defined(__linux__) && defined(__x86_64__)) \
-		|| (defined(ZEND_WIN32) && defined(_M_AMD64))
+#if ((defined(__linux__) && defined(__x86_64__)) \
+		|| (defined(ZEND_WIN32) && defined(_M_AMD64))) \
+		&& !defined(NO_ZEND_HIGH_HALF_KERNEL)
 /* The kernel reserves the higher part of the address space for itself.
  * Therefore, we can assume that the higher bit of user space addresses is
  * never set. */