switch to +vfp3d16 LLVM feature in armv7a-vex-v5

The Cortex-A9 only has 16 double-precision registers (`d0`-`d15`), so this is the correct VFP instructionset to use.

Author: Tropix126

compiler/rustc_target/src/spec/targets/armv7a_vex_v5.rs

@@ -21,7 +21,7 @@ pub(crate) fn target() -> Target {
             env: "v5".into(),
             cpu: "cortex-a9".into(),
             abi: "eabihf".into(),
-            features: "+v7,+neon,+vfp3,+thumb2".into(),
+            features: "+v7,+neon,+vfp3d16,+thumb2".into(),
             linker: Some("rust-lld".into()),
             linker_flavor: LinkerFlavor::Gnu(Cc::No, Lld::Yes),
             link_script: Some(LINK_SCRIPT.into()),