Rollup merge of rust-lang#35606 - Mark-Simulacrum:no-std-fix, r=brson

Change stabilization version of no_std from 1.0 to 1.6.

I don't know if more than this is needed.

Fixes rust-lang#35579.

Author: eddyb

src/libsyntax/feature_gate.rs

@@ -314,7 +314,7 @@ declare_features! (
     (accepted, issue_5723_bootstrap, "1.0.0", None),
     (accepted, macro_rules, "1.0.0", None),
     // Allows using #![no_std]
-    (accepted, no_std, "1.0.0", None),
+    (accepted, no_std, "1.6.0", None),
     (accepted, slicing_syntax, "1.0.0", None),
     (accepted, struct_variant, "1.0.0", None),
     // These are used to test this portion of the compiler, they don't actually