make sure that all specs define QMAKE_{PREFIX,EXTENSION}_{SH,STATIC}LIB,
and adjust the code to make halfways consistent use of these variables,
in particular on windows; Win32MakefileGenerator::getLibTarget() is gone
as a result, as is QMAKE_CYGWIN_SHLIB. still, tons of hardcoded "lib"
references remain in the unix generator, because no-one cares.
Change-Id: I6ccf37cc562f6584221c94fa27b2834412e4e4ca
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>
f734599629