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

Rollup of 9 pull requests

Successful merges:

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

Failed merges:

 - rust-lang/rust#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

compiler/rustc_session/src/options.rs

@@ -290,6 +290,14 @@ macro_rules! top_level_options {
                 mods.sort_by(|a, b| a.opt.cmp(&b.opt));
                 mods
             }
+
+            pub fn target_feature_flag_enabled(&self, flag: &str) -> bool {
+                match flag {
+                    "retpoline" => self.unstable_opts.retpoline,
+                    "retpoline-external-thunk" => self.unstable_opts.retpoline_external_thunk,
+                    _ => false,
+                }
+            }
         }
     );
 }
@@ -2448,6 +2456,11 @@ options! {
     remark_dir: Option<PathBuf> = (None, parse_opt_pathbuf, [UNTRACKED],
         "directory into which to write optimization remarks (if not specified, they will be \
 written to standard error output)"),
+    retpoline: bool = (false, parse_bool, [TRACKED TARGET_MODIFIER],
+        "enables retpoline-indirect-branches and retpoline-indirect-calls target features (default: no)"),
+    retpoline_external_thunk: bool = (false, parse_bool, [TRACKED TARGET_MODIFIER],
+        "enables retpoline-external-thunk, retpoline-indirect-branches and retpoline-indirect-calls \
+        target features (default: no)"),
     sanitizer: SanitizerSet = (SanitizerSet::empty(), parse_sanitizers, [TRACKED],
         "use a sanitizer"),
     sanitizer_cfi_canonical_jump_tables: Option<bool> = (Some(true), parse_opt_bool, [TRACKED],