qa/pmdas/dynamic/GNUmakefile.install: re-instate build for QA
qa/pmdas/dynamic/GNUmakefile.install: re-instate build for QA

Last round of changes stopped pmdadynamic being built during QA
and this one can be rebuilt safely in either the testsuite or the
build tree contexts.

This was causing qa/956 to fail pretty much everywhere for me.

tjanez/pcp,edwardt/pcp,aeg-aeg/pcpfans,prasincs/pcp,tjanez/pcp,tjanez/pcp,adfernandes/pcp,wuliming/pcp,edwardt/pcp,aeg-aeg/pcpfans,adfernandes/pcp,prasincs/pcp,wuliming/pcp,prasincs/pcp,adfernandes/pcp,edwardt/pcp,tjanez/pcp,tjanez/pcp,aeg-aeg/pcpfans,edwardt/pcp,prasincs/pcp,wuliming/pcp,tjanez/pcp,adfernandes/pcp,prasincs/pcp,tjanez/pcp,wuliming/pcp,edwardt/pcp,aeg-aeg/pcpfans,aeg-aeg/pcpfans,edwardt/pcp,aeg-aeg/pcpfans,wuliming/pcp,adfernandes/pcp,aeg-aeg/pcpfans,aeg-aeg/pcpfans,adfernandes/pcp,wuliming/pcp,prasincs/pcp,edwardt/pcp,adfernandes/pcp,wuliming/pcp,adfernandes/pcp,edwardt/pcp,wuliming/pcp,prasincs/pcp,tjanez/pcp,prasincs/pcp