Fix link failure on sparc-unknown-linux-gnu

Author: taiki-e

compiler/rustc_codegen_ssa/src/back/metadata.rs

@@ -401,6 +401,7 @@ pub(super) fn elf_e_flags(architecture: Architecture, sess: &Session) -> u32 {
                 _ => EF_PPC64_ABI_UNKNOWN,
             }
         }
+        Architecture::Sparc32Plus => elf::EF_SPARC_32PLUS,
         _ => 0,
     }
 }