Modifying sip_configure for improper lib names

[brawner]

This adds a check to sip_configure.py for whether the lib name is None, an empty string or whitespace.

For example, when I build qt_gui_cpp this is the diff for the qt_gui_cpp_sip.so Makefile if I ask CMakeLists to find_package(Boost...) (even if the code doesn't use it) and if I don't.

< With find_package(Boost)
> Without find_package(Boost)
< LIBS = -Flib -Llib -F/usr/local/Cellar/qt/5.11.2/lib -L/usr/local/Cellar/qt/5.11.2/lib /usr/local/lib/libboost_filesystem-mt.dylib /usr/local/lib/libboost_system-mt.dylib -framework QtCore -framework DiskArbitration -framework IOKit -framework QtGui -F$$[QT_INSTALL_LIBS] -framework QtCore -framework DiskArbitration -framework IOKit -framework QtWidgets -framework QtPrintSupport
---
> LIBS = -Flib -Llib -F/usr/local/Cellar/qt/5.11.2/lib -L/usr/local/Cellar/qt/5.11.2/lib -l -framework QtCore -framework DiskArbitration -framework IOKit -framework QtGui -F$$[QT_INSTALL_LIBS] -framework QtCore -framework DiskArbitration -framework IOKit -framework QtWidgets -framework QtPrintSupport

Or condensed:

< LIBS = -Flib -Llib ... libboost_system-mt.dylib -framework QtCore ...
---
> LIBS = -Flib -Llib ... qt/5.11.2/lib -l -framework QtCore...

And this is the line from the Makefile with this bug fix

< LIBS = -Flib -Llib ... qt/5.11.2/lib -framework QtCore ...