Remove unneeded features

A few of the features that we enable have been stabilized, others may
have been needed at some point but are no longer required. Clean this
up.

library/compiler-builtins/examples/intrinsics.rs

@@ -4,12 +4,10 @@
 // to link due to the missing intrinsic (symbol).
 
 #![allow(unused_features)]
-#![allow(stable_features)] // bench_black_box feature is stable, leaving for backcompat
 #![allow(internal_features)]
 #![cfg_attr(thumb, no_main)]
 #![deny(dead_code)]
 #![feature(allocator_api)]
-#![feature(bench_black_box)]
 #![feature(f128)]
 #![feature(f16)]
 #![feature(lang_items)]

library/compiler-builtins/src/lib.rs

@@ -1,18 +1,12 @@
 #![cfg_attr(feature = "compiler-builtins", compiler_builtins)]
-#![cfg_attr(not(feature = "no-asm"), feature(asm))]
 #![feature(abi_unadjusted)]
 #![feature(asm_experimental_arch)]
-#![cfg_attr(not(feature = "no-asm"), feature(global_asm))]
 #![feature(cfg_target_has_atomic)]
 #![feature(compiler_builtins)]
-#![feature(core_ffi_c)]
 #![feature(core_intrinsics)]
-#![feature(inline_const)]
-#![feature(lang_items)]
 #![feature(linkage)]
 #![feature(naked_functions)]
 #![feature(repr_simd)]
-#![feature(c_unwind)]
 #![cfg_attr(f16_enabled, feature(f16))]
 #![cfg_attr(f128_enabled, feature(f128))]
 #![no_builtins]

library/compiler-builtins/testcrate/tests/aeabi_memclr.rs

@@ -5,7 +5,6 @@
     feature = "mem"
 ))]
 #![feature(compiler_builtins_lib)]
-#![feature(lang_items)]
 #![no_std]
 
 extern crate compiler_builtins;

library/compiler-builtins/testcrate/tests/aeabi_memcpy.rs

@@ -5,7 +5,6 @@
     feature = "mem"
 ))]
 #![feature(compiler_builtins_lib)]
-#![feature(lang_items)]
 #![no_std]
 
 extern crate compiler_builtins;

library/compiler-builtins/testcrate/tests/aeabi_memset.rs

@@ -5,7 +5,6 @@
     feature = "mem"
 ))]
 #![feature(compiler_builtins_lib)]
-#![feature(lang_items)]
 #![no_std]
 
 extern crate compiler_builtins;