std.heap.rawCAlloc: avoid unecessary @Alignof

This was causing @Alignof to panic on FreeBSD, NetBSD and DragonflyBSD
x86_64 arch, as their system malloc returns memory aligned at 8 bytes
for len <= 8.

Author: mikdusan

lib/std/heap.zig

@@ -181,9 +181,7 @@ fn rawCAlloc(
 ) ?[*]u8 {
     _ = ret_addr;
     assert(log2_ptr_align <= comptime std.math.log2_int(usize, @alignOf(std.c.max_align_t)));
-    // TODO: change the language to make @ptrCast also do alignment cast
-    const ptr = @alignCast(@alignOf(std.c.max_align_t), c.malloc(len));
-    return @ptrCast(?[*]align(@alignOf(std.c.max_align_t)) u8, ptr);
+    return @ptrCast([*]u8, c.malloc(len));
 }
 
 fn rawCResize(