Auto merge of #142443 - matthiaskrgr:rollup-l1l6d0v, r=matthiaskrgr

Rollup of 9 pull requests

Successful merges:

 - #128425 (Make `missing_fragment_specifier` an unconditional error)
 - #135927 (retpoline and retpoline-external-thunk flags (target modifiers) to enable retpoline-related target features)
 - #140770 (add `extern "custom"` functions)
 - #142176 (tests: Split dont-shuffle-bswaps along opt-levels and arches)
 - #142248 (Add supported asm types for LoongArch32)
 - #142267 (assert more in release in `rustc_ast_lowering`)
 - #142274 (Update the stdarch submodule)
 - #142276 (Update dependencies in `library/Cargo.lock`)
 - #142308 (Upgrade `object`, `addr2line`, and `unwinding` in the standard library)

Failed merges:

 - #140920 (Extract some shared code from codegen backend target feature handling)

r? `@ghost`
`@rustbot` modify labels: rollup

try-job: aarch64-apple
try-job: x86_64-msvc-1
try-job: x86_64-gnu
try-job: dist-i586-gnu-i586-i686-musl
try-job: test-various

Author: bors

compiler/rustc_abi/src/canon_abi.rs

@@ -28,6 +28,9 @@ pub enum CanonAbi {
     Rust,
     RustCold,
 
+    /// An ABI that rustc does not know how to call or define.
+    Custom,
+
     /// ABIs relevant to 32-bit Arm targets
     Arm(ArmCall),
     /// ABI relevant to GPUs: the entry point for a GPU kernel
@@ -57,6 +60,7 @@ impl fmt::Display for CanonAbi {
             CanonAbi::C => ExternAbi::C { unwind: false },
             CanonAbi::Rust => ExternAbi::Rust,
             CanonAbi::RustCold => ExternAbi::RustCold,
+            CanonAbi::Custom => ExternAbi::Custom,
             CanonAbi::Arm(arm_call) => match arm_call {
                 ArmCall::Aapcs => ExternAbi::Aapcs { unwind: false },
                 ArmCall::CCmseNonSecureCall => ExternAbi::CCmseNonSecureCall,

compiler/rustc_abi/src/extern_abi.rs

@@ -40,6 +40,11 @@ pub enum ExternAbi {
     /// Even normally-compatible Rust types can become ABI-incompatible with this ABI!
     Unadjusted,
 
+    /// An ABI that rustc does not know how to call or define. Functions with this ABI can
+    /// only be created using `#[naked]` functions or `extern "custom"` blocks, and can only
+    /// be called from inline assembly.
+    Custom,
+
     /// UEFI ABI, usually an alias of C, but sometimes an arch-specific alias
     /// and only valid on platforms that have a UEFI standard
     EfiApi,
@@ -141,6 +146,7 @@ abi_impls! {
             AvrNonBlockingInterrupt =><= "avr-non-blocking-interrupt",
             Cdecl { unwind: false } =><= "cdecl",
             Cdecl { unwind: true } =><= "cdecl-unwind",
+            Custom =><= "custom",
             EfiApi =><= "efiapi",
             Fastcall { unwind: false } =><= "fastcall",
             Fastcall { unwind: true } =><= "fastcall-unwind",