Add target thumbv7neon-unknown-linux-musleabihf

This is a copy of thumbv7neon-unknown-linux-gnueabihf with musl changes
merged from armv7-unknown-linux-musleabihf.

src/librustc_target/spec/mod.rs

@@ -362,6 +362,7 @@ supported_targets! {
     ("armv7-unknown-linux-gnueabi", armv7_unknown_linux_gnueabi),
     ("armv7-unknown-linux-gnueabihf", armv7_unknown_linux_gnueabihf),
     ("thumbv7neon-unknown-linux-gnueabihf", thumbv7neon_unknown_linux_gnueabihf),
+    ("thumbv7neon-unknown-linux-musleabihf", thumbv7neon_unknown_linux_musleabihf),
     ("armv7-unknown-linux-musleabi", armv7_unknown_linux_musleabi),
     ("armv7-unknown-linux-musleabihf", armv7_unknown_linux_musleabihf),
     ("aarch64-unknown-linux-gnu", aarch64_unknown_linux_gnu),

src/librustc_target/spec/thumbv7neon_unknown_linux_musleabihf.rs

@@ -0,0 +1,37 @@
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
+
+// This target is for musl Linux on ARMv7 with thumb mode enabled
+// (for consistency with Android and Debian-based distributions)
+// and with NEON unconditionally enabled and, therefore, with 32 FPU
+// registers enabled as well. See section A2.6.2 on page A2-56 in
+// https://static.docs.arm.com/ddi0406/cd/DDI0406C_d_armv7ar_arm.pdf
+
+pub fn target() -> TargetResult {
+    let base = super::linux_musl_base::opts();
+    Ok(Target {
+        // It's important we use "gnueabihf" and not "musleabihf" here. LLVM
+        // uses it to determine the calling convention and float ABI, and LLVM
+        // doesn't support the "musleabihf" value.
+        llvm_target: "armv7-unknown-linux-gnueabihf".to_string(),
+        target_endian: "little".to_string(),
+        target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
+        data_layout: "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
+        arch: "arm".to_string(),
+        target_os: "linux".to_string(),
+        target_env: "musl".to_string(),
+        target_vendor: "unknown".to_string(),
+        linker_flavor: LinkerFlavor::Gcc,
+
+        // Most of these settings are copied from the thumbv7neon_unknown_linux_gnueabihf
+        // target.
+        options: TargetOptions {
+            features: "+v7,+thumb-mode,+thumb2,+vfp3,+neon".to_string(),
+            cpu: "generic".to_string(),
+            max_atomic_width: Some(64),
+            abi_blacklist: super::arm_base::abi_blacklist(),
+            target_mcount: "\u{1}mcount".to_string(),
+            .. base
+        }
+    })
+}