Add powerpc-unknown-linux-muslspe compile target

This is almost identical to already existing targets:
- powerpc_unknown_linux_musl.rs
- powerpc_unknown_linux_gnuspe.rs

It has support for PowerPC SPE (muslspe), which
can be used with GCC version up to 8. It is useful for Freescale or IBM
cores like e500.

This was verified to be working with OpenWrt build system for CZ.NIC's
Turris 1.x routers, which are using Freescale P2020, e500v2, so add it as
a Tier 3 target.

Author: BKPepe

compiler/rustc_target/src/spec/mod.rs

@@ -834,6 +834,7 @@ supported_targets! {
     ("powerpc-unknown-linux-gnu", powerpc_unknown_linux_gnu),
     ("powerpc-unknown-linux-gnuspe", powerpc_unknown_linux_gnuspe),
     ("powerpc-unknown-linux-musl", powerpc_unknown_linux_musl),
+    ("powerpc-unknown-linux-muslspe", powerpc_unknown_linux_muslspe),
     ("powerpc64-unknown-linux-gnu", powerpc64_unknown_linux_gnu),
     ("powerpc64-unknown-linux-musl", powerpc64_unknown_linux_musl),
     ("powerpc64le-unknown-linux-gnu", powerpc64le_unknown_linux_gnu),

compiler/rustc_target/src/spec/powerpc_unknown_linux_muslspe.rs

@@ -0,0 +1,21 @@
+use crate::abi::Endian;
+use crate::spec::{LinkerFlavor, Target, TargetOptions};
+
+pub fn target() -> Target {
+    let mut base = super::linux_musl_base::opts();
+    base.add_pre_link_args(LinkerFlavor::Gcc, &["-mspe"]);
+    base.max_atomic_width = Some(32);
+
+    Target {
+        llvm_target: "powerpc-unknown-linux-muslspe".into(),
+        pointer_width: 32,
+        data_layout: "E-m:e-p:32:32-i64:64-n32".into(),
+        arch: "powerpc".into(),
+        options: TargetOptions {
+            abi: "spe".into(),
+            endian: Endian::Big,
+            mcount: "_mcount".into(),
+            ..base
+        },
+    }
+}

src/doc/rustc/src/SUMMARY.md

@@ -27,6 +27,7 @@
     - [m68k-unknown-linux-gnu](platform-support/m68k-unknown-linux-gnu.md)
     - [mips64-openwrt-linux-musl](platform-support/mips64-openwrt-linux-musl.md)
     - [nvptx64-nvidia-cuda](platform-support/nvptx64-nvidia-cuda.md)
+    - [powerpc-unknown-linux-muslspe](platform-support/powerpc-unknown-linux-muslspe.md)
     - [riscv32imac-unknown-xous-elf](platform-support/riscv32imac-unknown-xous-elf.md)
     - [*-pc-windows-gnullvm](platform-support/pc-windows-gnullvm.md)
     - [*-unknown-openbsd](platform-support/openbsd.md)

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

@@ -266,6 +266,7 @@ target | std | host | notes
 `msp430-none-elf` | * |  | 16-bit MSP430 microcontrollers
 `powerpc-unknown-linux-gnuspe` | ✓ |  | PowerPC SPE Linux
 `powerpc-unknown-linux-musl` | ? |  |
+[`powerpc-unknown-linux-muslspe`](platform-support/powerpc-unknown-linux-muslspe.md) | ? |  | PowerPC SPE Linux
 `powerpc-unknown-netbsd` | ✓ | ✓ |
 `powerpc-unknown-openbsd` | ? |  |
 `powerpc-wrs-vxworks-spe` | ? |  |

src/doc/rustc/src/platform-support/powerpc-unknown-linux-muslspe.md

@@ -0,0 +1,32 @@
+# powerpc-unknown-linux-muslspe
+
+**Tier: 3**
+
+This target is very similar to already existing ones like `powerpc_unknown_linux_musl` and `powerpc_unknown_linux_gnuspe`.
+This one has PowerPC SPE support for musl. Unfortunately, the last supported gcc version with PowerPC SPE is 8.4.0.
+
+## Target maintainers
+
+- [@BKPepe](https://github.com/BKPepe)
+
+## Requirements
+
+This target is cross-compiled. There is no support for `std`. There is no
+default allocator, but it's possible to use `alloc` by supplying an allocator.
+
+This target generated binaries in the ELF format.
+
+## Building the target
+
+This target was tested and used within the `OpenWrt` build system for CZ.NIC Turris 1.x routers using Freescale P2020.
+
+## Building Rust programs
+
+Rust does not yet ship pre-compiled artifacts for this target. To compile for
+this target, you will either need to build Rust with the target enabled (see
+"Building the target" above), or build your own copy of `core` by using
+`build-std` or similar.
+
+## Testing
+
+This is a cross-compiled target and there is no support to run rustc test suite.