Log Message:
waf: update to 2.0.19.

Fix a pkglint warning.

NEW IN WAF 2.0.19
-----------------
* Enable race-free pdb file generation waflib/extras/msvc_pdb.py #1731
* Fix negative values for -j #2256
* Fix Swig example compatibility with Python3 #2259
* Fix lto settings for endianness configuration tests #2250
* Tune the application name on --help #2254
* Improve Qt5's fPIC/fPIE detection
* Propagate LDFLAGS to Fortran tasks (in addition to LINKFLAGS)
* Enable local and remote build object caches waflib/extras/wafcache.py