message: add option to build crate within libstd
diff: @@ -24,8 +24,11 @@ crate-type = ["staticlib", "rlib"]
  [features]
  vga = []
  newlib = []
  +rustc-dep-of-std = ['core', 'compiler_builtins/rustc-dep-of-std']
  [dependencies]
  +core = { version = '1.0.0', optional = true, package = 'rustc-std-workspace-core' }
  +compiler_builtins = { version = '0.1.10', optional = true }
  bitflags = "1.2"
  #cfg-if = "0.1"
  #byteorder = { version = "1.0", default-features = false }
  