heap: make page size work with macos

Author: RossComputerGuy

lib/std/c/darwin.zig

@@ -3693,7 +3693,7 @@ pub const MachTask = extern struct {
         return left;
     }
 
-    fn getPageSize(task: MachTask) MachError!usize {
+    pub fn getPageSize(task: MachTask) MachError!usize {
         if (task.isValid()) {
             var info_count = TASK_VM_INFO_COUNT;
             var vm_info: task_vm_info_data_t = undefined;
@@ -3846,3 +3846,5 @@ pub extern "c" fn os_signpost_interval_begin(log: os_log_t, signpos: os_signpost
 pub extern "c" fn os_signpost_interval_end(log: os_log_t, signpos: os_signpost_id_t, func: [*]const u8, ...) void;
 pub extern "c" fn os_signpost_id_make_with_pointer(log: os_log_t, ptr: ?*anyopaque) os_signpost_id_t;
 pub extern "c" fn os_signpost_enabled(log: os_log_t) bool;
+
+pub extern "c" fn getpagesize() c_int;

lib/std/heap.zig

@@ -584,7 +584,8 @@ pub fn pageSize() usize {
     if (page_size) |pg_size| return pg_size;
     page_size = switch (builtin.os.tag) {
         .linux => if (builtin.link_libc) @intCast(std.c.sysconf(std.os.linux.SC.PAGESIZE)) else std.os.linux.getauxval(std.elf.AT_PAGESZ),
-        else => mem.page_size,
+        .macos => std.os.darwin.machTaskForSelf().getPageSize() catch mem.page_size,
+        else => if (builtin.link_libc and @hasDecl(std.c, "getpagesize")) std.c.getpagesize() else mem.page_size,
     };
     return page_size.?;
 }