fix EXE_SUFFFIX to use dot

Author: Tropix126

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

@@ -17,7 +17,7 @@ pub(crate) fn target() -> Target {
         options: TargetOptions {
             os: "vexos".into(),
             vendor: "vex".into(),
-            exe_suffix: "elf".into(),
+            exe_suffix: ".elf".into(),
             cpu: "cortex-a9".into(),
             abi: "eabihf".into(),
             features: "+v7,+neon,+vfp3,+thumb2,+thumb-mode".into(),