target: support scalable vectors on arm64ec

This architecture is also AArch64, just with a different ABI, and so
supports scalable vectors too.

Author: davidtwco

compiler/rustc_target/src/spec/mod.rs

@@ -1957,8 +1957,8 @@ impl Arch {
         use Arch::*;
 
         match self {
-            AArch64 | RiscV32 | RiscV64 => true,
-            AmdGpu | Arm | Arm64EC | Avr | Bpf | CSky | Hexagon | LoongArch32 | LoongArch64
+            Arm64EC | AArch64 | RiscV32 | RiscV64 => true,
+            AmdGpu | Arm | Avr | Bpf | CSky | Hexagon | LoongArch32 | LoongArch64
             | M68k | Mips | Mips32r6 | Mips64 | Mips64r6 | Msp430 | Nvptx64 | PowerPC
             | PowerPC64 | S390x | Sparc | Sparc64 | SpirV | Wasm32 | Wasm64 | X86 | X86_64
             | Xtensa | Other(_) => false,