rustc: Implement the #[global_allocator] attribute

This PR is an implementation of [RFC 1974] which specifies a new method of
defining a global allocator for a program. This obsoletes the old
`#![allocator]` attribute and also removes support for it.

[RFC 1974]: https://github.com/rust-lang/rfcs/pull/197

The new `#[global_allocator]` attribute solves many issues encountered with the
`#![allocator]` attribute such as composition and restrictions on the crate
graph itself. The compiler now has much more control over the ABI of the
allocator and how it's implemented, allowing much more freedom in terms of how
this feature is implemented.

cc #27389

1 files changed, 1 insertions, 0 deletions

diff --git a/src/librustc_llvm/ffi.rs b/src/librustc_llvm/ffi.rs
index 770d16e5c02..9f0ee95b5a6 100644
--- a/src/librustc_llvm/ffi.rs
+++ b/src/librustc_llvm/ffi.rs
@@ -698,6 +698,7 @@ extern "C" {
     pub fn LLVMIsGlobalConstant(GlobalVar: ValueRef) -> Bool;
     pub fn LLVMSetGlobalConstant(GlobalVar: ValueRef, IsConstant: Bool);
     pub fn LLVMRustGetNamedValue(M: ModuleRef, Name: *const c_char) -> ValueRef;
+    pub fn LLVMSetTailCall(CallInst: ValueRef, IsTailCall: Bool);
 
     // Operations on functions
     pub fn LLVMAddFunction(M: ModuleRef, Name: *const c_char, FunctionTy: TypeRef) -> ValueRef;