rust: Rust-ABI dynamic libraries do not support LTO

Attempting to use LTO on e.g. a procedural macro crate fails with

  error: lto cannot be used for proc-macro crate type without -Zdylib-lto

Do not return -Clto for such crate types.

Signed-off-by: Paolo Bonzini <[email protected]>

Author: bonzini

mesonbuild/compilers/rust.py

@@ -367,6 +367,9 @@ def get_embed_bitcode_args(self, bitcode: bool, lto: bool) -> T.List[str]:
 
     def get_lto_compile_args(self, *, target: T.Optional[BuildTarget] = None, threads: int = 0,
                              mode: str = 'default') -> T.List[str]:
+        if target.rust_crate_type in {'dylib', 'proc-macro'}:
+            return []
+
         # TODO: what about -Clinker-plugin-lto?
         rustc_lto = 'lto=thin' if mode == 'thin' else 'lto'
         return ['-C', rustc_lto]