Error caused by compiler_builtins_lib
I had a build error on Ubuntu 18.04 64bit because rust didn't like #![feature(compiler_builtins_lib)] . Looking around I found a solution to include #![no_std] as per the following git diff
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index cfee49a7b55..b39a4712f69 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -246,7 +246,8 @@
#![feature(char_error_internals)]
#![feature(checked_duration_since)]
#![feature(clamp)]
-#![feature(compiler_builtins_lib)]
+//#![feature(compiler_builtins_lib)]
+#![no_std]
#![feature(concat_idents)]
#![feature(const_cstr_unchecked)]
#![feature(const_raw_ptr_deref)]