Rollup merge of rust-lang#132421 - beetrees:riscv-abi-no-empty-string, r=workingjubilee

Remove `""` case from RISC-V `llvm_abiname` match statement

For RISC-V, `""` isn't the always the same ABI as `"ilp32"`/`"lp64"` (`""` means LLVM will infer the ABI based on the enabled target features), but `create_object_file` currently assumes that it is. Since all RISC-V targets explicitly specify their ABI since rust-lang#131807, this PR removes `""` from the match arm's pattern (meaning an empty string will now fall through to the `_ => bug!` arm).

r? `@workingjubilee`

Author: workingjubilee

compiler/rustc_codegen_ssa/src/back/metadata.rs

@@ -322,7 +322,7 @@ pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static
             // Set the appropriate flag based on ABI
             // This needs to match LLVM `RISCVELFStreamer.cpp`
             match &*sess.target.llvm_abiname {
-                "" | "ilp32" | "lp64" => (),
+                "ilp32" | "lp64" => (),
                 "ilp32f" | "lp64f" => e_flags |= elf::EF_RISCV_FLOAT_ABI_SINGLE,
                 "ilp32d" | "lp64d" => e_flags |= elf::EF_RISCV_FLOAT_ABI_DOUBLE,
                 // Note that the `lp64e` is still unstable as it's not (yet) part of the ELF psABI.