Move style-check to separate script

This avoids having to copy out of .gitlab-ci.yml before submitting an MR
to do a style check.

Could become a meson target at some point.

tools/style-check

@@ -0,0 +1,13 @@
+#!/bin/sh
+
+if [ -z "$1" ]; then
+    echo "Please pass directory to check."
+    exit 1
+fi
+
+cd "$1"
+clang-tidy --checks=-clang-diagnostic-missing-braces,readability-braces-around-statements, \
+           --warnings-as-errors=readability-braces-around-statements \
+           -extra-arg=-Wno-unknown-warning-option \
+           ../src/*.c ../eek/*.c ../eekboard/*.c
+