X11/qt5-qscintilla: fix install_name on Darwin

[Brook Milligan <brook%nmsu.edu@localhost>]

I am trying to get x11/qt5-qscintilla to build on Darwin.  It turns out that during the configure phase, qmake creates a link command that includes “-install_name libqscintilla2…”.  The problem is that this introduces a relative path into the library.  The correct command would include “-install_name ${PREFIX}/libqscintilla2…”. 

I can achieve this with the following Makefile fragment:

SUBST_CLASSES+=			install_name
SUBST_STAGE.install_name=	post-configure
SUBST_FILES.install_name=	Makefile
SUBST_SED.install_name	=	-e "s,\(-install_name	\)\(libqscintilla2_qt5.15.dylib\),\1${PREFIX}/qt5/lib\2,”

However, I fear that this will be a recurring problem with the way qmake configures Makefile commands on Darwin, and that a better solution would be to address that.

Unfortunately, I have no idea how qmake works and cannot find where it actually generates the command.

If anyone has knowledge or suggestions, please speak up.

Thanks.

Cheers,
Brook