Make profiler_builtins #![no_core] instead of just #![no_std]

This crate doesn't contain any actual Rust code; it's just C/C++ code built and
packaged in a Rust-friendly way.

library/Cargo.lock

@@ -235,8 +235,6 @@ name = "profiler_builtins"
 version = "0.0.0"
 dependencies = [
  "cc",
- "compiler_builtins",
- "core",
 ]
 
 [[package]]

library/profiler_builtins/Cargo.toml

@@ -9,8 +9,6 @@ bench = false
 doc = false
 
 [dependencies]
-core = { path = "../core" }
-compiler_builtins = { version = "0.1.0", features = ['rustc-dep-of-std'] }
 
 [build-dependencies]
 # FIXME: Pinned due to build error when bumped (#132556)

library/profiler_builtins/src/lib.rs

@@ -1,11 +1,12 @@
 // tidy-alphabetical-start
 #![allow(internal_features)]
+#![feature(no_core)]
 #![feature(profiler_runtime)]
 #![feature(staged_api)]
 // tidy-alphabetical-end
 
 // Other attributes:
-#![no_std]
+#![no_core]
 #![profiler_runtime]
 #![unstable(
     feature = "profiler_runtime_lib",