gen_compile_commands: fix missing 'sys' package

We need to import the 'sys' package since the script has called
sys.exit() method.

Fixes: 6ad7cbc01527 ("Makefile: Add clang-tidy and static analyzer support to makefile")
Signed-off-by: Kortan <[e-mail]>
Reviewed-by: Nathan Chancellor <[e-mail]>
Signed-off-by: Masahiro Yamada <[e-mail]>

scripts/clang-tools/gen_compile_commands.py

···
 import os
 import re
 import subprocess
+import sys
 
 _DEFAULT_OUTPUT = 'compile_commands.json'
 _DEFAULT_LOG_LEVEL = 'WARNING'