request to change x11/qt5-qtbase dependencies

[Niclas Rosenvik <nros%netbsd.org@localhost>]

I would like to make qt5-qtbase dependent on math/double-conversion and textproc/md4c.
qt5-qtbase uses these libraries but does build the bundled ones currently.
qt5-qtbase includes a patch to double-conversion
"patch-src_3rdparty_double-conversion_include_double-conversion_utils.h"
that I would like to move over to math/double-conversion thinking it
would help double-conversion to build correctly on sh cpu:s. I am
writing on tech-pkg since I couldn't find the email address to the pmc
and others might have an opinion about this. The qt5 packages seem to
be in a constant freeze according to the freeze policies and the
proposed change could affect its stability. Yes, I have tested to build
qt5-qtbase with the changes and it builds without problems for me on
NetBSD-9 x86-64.

Niclas