std: move auto_align constant to top of comptime function

At a later point in time this might be made into a parameter

lib/std/fifo.zig

@@ -10,6 +10,8 @@ const assert = debug.assert;
 const testing = std.testing;
 
 pub fn FixedSizeFifo(comptime T: type) type {
+    const autoalign = false;
+
     return struct {
         allocator: *Allocator,
         buf: []T,
@@ -107,8 +109,6 @@ pub fn FixedSizeFifo(comptime T: type) type {
             return self.readableSliceMut(offset);
         }
 
-        const autoalign = false;
-
         /// Discard first `count` bytes of readable data
         pub fn discard(self: *Self, count: usize) void {
             assert(count <= self.count);