qgis: Update to 2.18.17

[ryandesign (Ryan Carsten Schmidt)]

This patch:

• updates qgis to 2.18.17
• updates to the cmake 1.1 portgroup which does out of source builds by default, and removes all the code from the portfile that manually did an out of source build (see #47197), and removes settings that the cmake portgroup sets for you
• uses the compiler_blacklist_versions 1.0 portgroup to blacklist clang < 500 rather than implementing that manually
• uses the cxx11 1.1 portgroup since qgis now requires C++11 (see #55863)
• uses the github 1.0 portgroup and removes all the code from the portfile that implemented it manually
• moves the homepage line down to where it is in the qgis3 portfile
• adds your GitHub handle to the maintainers line
• removes use_parallel_build no and use_parallel_build yes lines since yes is already the default
• moves patchfiles directive to be before the post-patch block
• adds size to checksums
• replaces ambiguous @@@ placeholder in patchfile with @PREFIX@ to match qgis3 port
• introduces new portfile variable grass_version and new patchfile placeholder @GRASS_VERSION@ so that it is no longer necessary to manually update the grass version in more than one place (we've forgotten to update it in all places before)
• updates grass version to 7.4.0 in grass variant

It compiles for me on Sierra and the app launches. I haven't tested more than that.

[Ryan Schmidt <git@…>]

In 8e7b757b819825f579032aba7c911dfb383d34b8/macports-ports:

qgis: Use compiler_blacklist_versions portgroup

…instead of implementing the functionality manually.

See: #55905

[Ryan Schmidt <git@…>]

In 368722d3cfc08f8bb213ac835a2557f39cf22f2d/macports-ports:

qgis: Introduce grass_version variable

See: #55905

[Ryan Schmidt <git@…>]

In 0844d0206b5b3271e7dd3bbb48a62c23bc921bf7/macports-ports:

qgis: Rename placeholder to @PREFIX@

…from the more ambiguous @@@

See: #55905

[Ryan Schmidt <git@…>]

In 56629204144b2f28919a668c943d1f76789087ea/macports-ports:

qgis: Add GitHub handle to maintainers

See: #55905

[Ryan Schmidt <git@…>]

In 4a5bb470565259b502fdc46d9ded9bd5bfc7a054/macports-ports:

qgis: Remove conflicting use_parallel_build directives

See: #55905

[Ryan Schmidt <git@…>]

In e8822a33971934d6587492b3f65865b46fa002d7/macports-ports:

qgis: Use cmake 1.1 portgroup

See: #55905
See: #47197

[Ryan Schmidt <git@…>]

In fb0d55386bf0e4c7d7e2935186e9ae3754bf01f5/macports-ports:

qgis: Move patchfiles near post-patch block

See: #55905

[Ryan Schmidt <git@…>]

In 4f50e85e854d4746d7b28cab89e73764b3d72581/macports-ports:

qgis: Move homepage under license

See: #55905

[Ryan Schmidt <git@…>]

In e09649eedebf75415e257e3a0b3a10a8b257b9c2/macports-ports:

qgis: Update to 2.18.17

Closes: #55905