Import GTK in preparation for rules_python

We currently import GTK libraries as part of the "python_gtk" repo.
That pulls in GTK, but also Python and a bunch of pip packages.

This patch makes it so that GTK is pulled in via a dedicated repo.
That allows us to have dedicated repos for pip packages via
rules_python.

Future patches will make use of the new GTK import.

I had to modify `download_packages.py` in order to ensure that `libc6`
really got excluded from the final tarball. On James' personal
machines, he observed stack smashing crashes when `libc` is in the
tarball. The `force_includes` usage pulled in `libc6` even though we
don't want it to.

Signed-off-by: Philipp Schrader <philipp.schrader@gmail.com>
Change-Id: Ia3ecf51e4bd4c7aa0e72646e4c2af738f6086c01
diff --git a/WORKSPACE b/WORKSPACE
index 172e7bb..dbde661 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -56,6 +56,10 @@
     python_gtk_debs = "files",
 )
 load(
+    "//debian:gtk_runtime.bzl",
+    gtk_runtime_debs = "files",
+)
+load(
     "//debian:opencv_arm64.bzl",
     opencv_arm64_debs = "files",
 )
@@ -127,6 +131,8 @@
 
 generate_repositories_for_debs(python_gtk_debs)
 
+generate_repositories_for_debs(gtk_runtime_debs)
+
 generate_repositories_for_debs(opencv_arm64_debs)
 
 generate_repositories_for_debs(opencv_armhf_debs)
@@ -683,6 +689,13 @@
     url = "https://www.frc971.org/Build-Dependencies/python_gtk-4.tar.gz",
 )
 
+http_archive(
+    name = "gtk_runtime",
+    build_file = "@//debian:gtk_runtime.BUILD",
+    sha256 = "934693e64bfe63f0c55cdf432fe183eb077d6875d4d6a3dce4e47dbe7e20f5a9",
+    url = "https://www.frc971.org/Build-Dependencies/gtk_runtime-3.tar.gz",
+)
+
 # Downloaded from
 # https://developer.arm.com/-/media/Files/downloads/gnu-rm/7-2018q2/gcc-arm-none-eabi-7-2018-q2-update-linux.tar.bz2?revision=bc2c96c0-14b5-4bb4-9f18-bceb4050fee7?product=GNU%20Arm%20Embedded%20Toolchain,64-bit,,Linux,7-2018-q2-update
 http_archive(