Add support for targeting riscv32im-unknown-none-elf

Update riscv32im-unknown-none-elf to Tier2 support.

Downgrade to Tier 3 platform support.

compiler/rustc_target/src/spec/mod.rs

@@ -975,6 +975,7 @@ supported_targets! {
     ("x86_64-unknown-none-hermitkernel", x86_64_unknown_none_hermitkernel),
 
     ("riscv32i-unknown-none-elf", riscv32i_unknown_none_elf),
+    ("riscv32im-unknown-none-elf", riscv32im_unknown_none_elf),
     ("riscv32imc-unknown-none-elf", riscv32imc_unknown_none_elf),
     ("riscv32imc-esp-espidf", riscv32imc_esp_espidf),
     ("riscv32imac-unknown-none-elf", riscv32imac_unknown_none_elf),

compiler/rustc_target/src/spec/riscv32im_unknown_none_elf.rs

@@ -0,0 +1,26 @@
+use crate::spec::{LinkerFlavor, LldFlavor, PanicStrategy, RelocModel};
+use crate::spec::{Target, TargetOptions};
+
+pub fn target() -> Target {
+    Target {
+        data_layout: "e-m:e-p:32:32-i64:64-n32-S128".to_string(),
+        llvm_target: "riscv32".to_string(),
+        pointer_width: 32,
+        arch: "riscv32".to_string(),
+
+        options: TargetOptions {
+            linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),
+            linker: Some("rust-lld".to_string()),
+            cpu: "generic-rv32".to_string(),
+            max_atomic_width: Some(0),
+            atomic_cas: false,
+            features: "+m".to_string(),
+            executables: true,
+            panic_strategy: PanicStrategy::Abort,
+            relocation_model: RelocModel::Static,
+            emit_debug_gdb_scripts: false,
+            eh_frame_header: false,
+            ..Default::default()
+        },
+    }
+}

src/doc/rustc/src/platform-support.md

@@ -271,6 +271,7 @@ target | std | host | notes
 `powerpc64le-unknown-linux-musl` | ? |  |
 `riscv32gc-unknown-linux-gnu` |   |   | RISC-V Linux (kernel 5.4, glibc 2.33)
 `riscv32gc-unknown-linux-musl` |   |   | RISC-V Linux (kernel 5.4, musl + RISCV32 support patches)
+`riscv32im-unknown-none-elf` | * |  | Bare RISC-V (RV32IM ISA)
 `riscv32imc-esp-espidf` | ✓ |  | RISC-V ESP-IDF
 `riscv64gc-unknown-freebsd` |   |   | RISC-V FreeBSD
 `riscv64gc-unknown-linux-musl` |   |   | RISC-V Linux (kernel 4.20, musl 1.2.0)

src/tools/build-manifest/src/main.rs

@@ -117,6 +117,7 @@ static TARGETS: &[&str] = &[
     "powerpc64-unknown-linux-gnu",
     "powerpc64le-unknown-linux-gnu",
     "riscv32i-unknown-none-elf",
+    "riscv32im-unknown-none-elf",
     "riscv32imc-unknown-none-elf",
     "riscv32imac-unknown-none-elf",
     "riscv32gc-unknown-linux-gnu",