Fix target-cpu fpu features on Armv8-R.

This is a follow-up to #123159, but applied to Armv8-R.

This required llvm/llvm-project#88287 to work
properly. Now that this change exists in rustc's llvm, we can fix
Armv8-R's default fpu features.

Add a run-make test that target-cpu=cortex-r52 enables double-precision
and neon.

compiler/rustc_target/src/spec/targets/armv8r_none_eabihf.rs

@@ -30,7 +30,7 @@ pub(crate) fn target() -> Target {
             // Reference:
             // Arm Cortex-R52 Processor Technical Reference Manual
             // - Chapter 15 Advanced SIMD and floating-point support
-            features: "+fp-armv8,-fp64,-d32".into(),
+            features: "+fp-armv8d16sp".into(),
             max_atomic_width: Some(64),
             emit_debug_gdb_scripts: false,
             // GCC defaults to 8 for arm-none here.

tests/run-make/arm-target-cpu-fp/armv8r_none_eabihf.checks

@@ -0,0 +1,10 @@
+// CHECK-LABEL: vadd_q:
+// CHECK: vld{{.*}}
+// CHECK: vld{{.*}}
+// CHECK: vadd.f32{{.*}}q
+// CHECK: vst{{.*}} [r0]
+// CHECK: bx lr
+
+// CHECK-LABEL: vadd_f64:
+// CHECK: vadd.f64 d0, d0, d1
+// CHECK: bx lr

tests/run-make/arm-target-cpu-fp/lib.rs

@@ -0,0 +1,13 @@
+#![no_std]
+
+#[no_mangle]
+pub fn vadd_q(x: &mut [f32; 4], y: &[f32; 4]) {
+    for i in 0..4 {
+        x[i] += y[i];
+    }
+}
+
+#[no_mangle]
+pub fn vadd_f64(x: f64, y: f64) -> f64 {
+    x + y
+}

tests/run-make/arm-target-cpu-fp/rmake.rs

@@ -0,0 +1,27 @@
+// This tests that target-cpu=cortex-r52 correctly enables double-precision and neon.
+
+use run_make_support::{llvm_filecheck, llvm_objdump, rustc, static_lib_name};
+
+fn main() {
+    let lib = static_lib_name("lib");
+
+    rustc()
+        .edition("2021")
+        .arg("--target=armv8r-none-eabihf")
+        .arg("-Ctarget-cpu=cortex-r52")
+        .arg("-Copt-level=3")
+        .crate_type("rlib")
+        .input("lib.rs")
+        .output(&lib)
+        .run();
+
+    let dis = llvm_objdump()
+        .arg("--arch-name=arm")
+        .arg("--mcpu=cortex-r52")
+        .disassemble()
+        .input(&lib)
+        .run()
+        .stdout_utf8();
+
+    llvm_filecheck().patterns("armv8r_none_eabihf.checks").stdin_buf(dis).run();
+}