patch 8.0.1572: Mac: getting memory size doesn't work everywhere

Problem:    Mac: getting memory size doesn't work everywhere.
Solution:   Use MACOS_X instead of MACOS_X_DARWIN. (Kazunobu Kuriyama)

src/os_unix.c

@@ -563,7 +563,7 @@ mch_check_messages(void)
 # if defined(HAVE_SYS_SYSINFO_H) && defined(HAVE_SYSINFO)
 #  include <sys/sysinfo.h>
 # endif
-# ifdef MACOS_X_DARWIN
+# ifdef MACOS_X
 #  include <mach/mach_host.h>
 #  include <mach/mach_port.h>
 # endif
@@ -578,7 +578,7 @@ mch_total_mem(int special UNUSED)
     long_u	mem = 0;
     long_u	shiftright = 10;  /* how much to shift "mem" right for Kbyte */
 
-# ifdef MACOS_X_DARWIN
+# ifdef MACOS_X
     {
 	/* Mac (Darwin) way of getting the amount of RAM available */
 	mach_port_t		host = mach_host_self();

src/version.c

@@ -766,6 +766,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1572,
 /**/
     1571,
 /**/