builtin/gc: correct physical memory detection for OpenBSD / NetBSD

OpenBSD / NetBSD use HW_PHYSMEM64 to detect the amount of physical
memory in a system. HW_PHYSMEM will not provide the correct amount
on a system with >=4GB of memory.

Signed-off-by: Brad Smith <brad@comstyle.com>
Reviewed-by: Collin Funk <collin.funk1@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: brad0

builtin/gc.c

@@ -516,14 +516,16 @@ static uint64_t total_ram(void)
 			total *= (uint64_t)si.mem_unit;
 		return total;
 	}
-#elif defined(HAVE_BSD_SYSCTL) && (defined(HW_MEMSIZE) || defined(HW_PHYSMEM))
+#elif defined(HAVE_BSD_SYSCTL) && (defined(HW_MEMSIZE) || defined(HW_PHYSMEM) || defined(HW_PHYSMEM64))
 	int64_t physical_memory;
 	int mib[2];
 	size_t length;
 
 	mib[0] = CTL_HW;
 # if defined(HW_MEMSIZE)
 	mib[1] = HW_MEMSIZE;
+# elif defined(HW_PHYSMEM64)
+	mib[1] = HW_PHYSMEM64;
 # else
 	mib[1] = HW_PHYSMEM;
 # endif