Ensure that semver files are sorted as part of CI

(backport <rust-lang#4018>)
(cherry picked from commit accd3b2)

ci/style.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env sh
+#!/bin/sh
 
 set -ex
 
@@ -18,3 +18,13 @@ else
     exit 1
 fi
 
+for file in libc-test/semver/*.txt; do
+    case "$file" in 
+      *TODO*) continue ;;
+    esac
+
+    if ! sort -C "$file"; then
+        echo "Unsorted semver file $file"
+        exit 1
+    fi
+done