gnu: qtbase: Use the store paths for other packages and dynamically loaded libs.

gnu: qtbase: Use the store paths for other packages and dynamically loaded libs.

Transfer the applicable NixOS patches as of 2018-01-19:

- Not adopted: We don't change the .cmake.in and .prf, but use config
  mechanisms provided by th Qt build system.

- src/corelib/tools/qtimezoneprivate_tz.cpp: Adopted patch: Use $TZDIR to
  search for time-zone data. Thus avoid depending on package "tzdata", which
  often introduces changes with near-immediate effects, so it's important to
  be able to update it fast.

- src/corelib/kernel/qcoreapplication.cpp: Not adopted: NixOS adds plugin
  paths derived from PATH. We do not need this, since we already have
  native-search-path QT_PLUGIN_PATH.

- src/network/kernel/qdnslookup_unix.cpp,
  src/network/kernel/qhostinfo_unix.cpp: Transferred: Use hard-coded path to
  libresolv.

- src/network/ssl/qsslcontext_openssl.cpp: Not adopted: NixOS changes a
  conditional compilation for Qt 5.9 (but leaves it unchanged for Qt 5.10) to
  fix compilation with libressl.  But Qt does not support libressl anway, see
  config.tests/openssl/openssl.cpp in qtbase 5.9.4.

- src/plugins/platforminputcontexts/compose/generator/qtablegenerator.cpp:
  Transferred: Use hard-coded path to libx11.

- src/plugins/platforms/xcb/gl_integrations/xcb_glx/qglxintegration.cpp:
  Transferred: Use hard-coded path to mess's libGL, no need for a fall-back.

- src/plugins/platforms/xcb/qxcbcursor.cpp: Transferred: Use hard-coded path
  to Xcursor.

- src/plugins/platformthemes/gtk3/main.cpp: Not adopted: NixOS changes
  $XDG_DATA_DIRS and $GIO_EXTRA_MODULES in the code. We already have a
  search-path-specification for this.

- src/testlib/qtestassert.h: Decided not to adopt this for guix.

* gnu/packages/patches/qtbase-use-TZDIR.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/qt.scm (qtbase): Add comment. [source]: Use new patch.
  [arguments]<#:phases>'patch-paths': New phase.