This commit re-enables the keep_last_cmd member variable in the TaskBase class
(which was disabled by default in Waf 2.0.9) when clang_compilation_database.py
is used. The clang_compilation_database.py file was correctly updated in the
relevant Waf commit introducing the change [1], but is missing in ns-3's bundled
version of Waf.
[1] 7778868718
Changes:
* run_c_code() is replaced by check()
* nice_path() got removed, and is replaced by bldpath()
* check_compilation_flag() is updated to work with 1.8 API