std: use decl literals to improve endian ergonomics

lib/std/builtin.zig

@@ -841,6 +841,9 @@ pub const FloatMode = enum {
 pub const Endian = enum {
     big,
     little,
+
+    pub const native = builtin.target.cpu.arch.endian();
+    pub const foreign: Endian = @enumFromInt(1 - @intFromEnum(native));
 };
 
 /// This data structure is used by the Zig language code generation and

lib/std/mem.zig

@@ -2006,11 +2006,13 @@ fn readPackedIntBig(comptime T: type, bytes: []const u8, bit_offset: usize) T {
     } else return @as(T, @bitCast(val));
 }
 
+/// Deprecated: use readPackedInt(T, bytes, bit_offset, value, .native)
 pub const readPackedIntNative = switch (native_endian) {
     .little => readPackedIntLittle,
     .big => readPackedIntBig,
 };
 
+/// Deprecated: use readPackedInt(T, bytes, bit_offset, value, .foreign)
 pub const readPackedIntForeign = switch (native_endian) {
     .little => readPackedIntBig,
     .big => readPackedIntLittle,
@@ -2159,11 +2161,13 @@ fn writePackedIntBig(comptime T: type, bytes: []u8, bit_offset: usize, value: T)
     writeInt(StoreInt, write_bytes[(byte_count - store_size)..][0..store_size], write_value, .big);
 }
 
+/// Deprecated: use writePackedInt(T, bytes, bit_offset, value, .native)
 pub const writePackedIntNative = switch (native_endian) {
     .little => writePackedIntLittle,
     .big => writePackedIntBig,
 };
 
+/// Deprecated: use writePackedInt(T, bytes, bit_offset, value, .foreign)
 pub const writePackedIntForeign = switch (native_endian) {
     .little => writePackedIntBig,
     .big => writePackedIntLittle,