Merge branch 'fix-empty-compile-commands-file' into 'master'

Fix empty compile_commands.json

See merge request nsnam/ns-3-dev!5

waf-tools/clang_compilation_database.py

@@ -15,9 +15,11 @@ Usage:
 """
 
 import sys, os, json, shlex, pipes
-from waflib import Logs, TaskGen
+from waflib import Logs, TaskGen, Task
 from waflib.Tools import c, cxx
 
+Task.TaskBase.keep_last_cmd = True
+
 if sys.hexversion >= 0x3030000:
 	quote = shlex.quote
 else: