ci: Shift to a prebuilt Docker image

.travis.yml

@@ -88,7 +88,7 @@ script:
         --rm \
         --workdir /travis \
         --volume ${TRAVIS_BUILD_DIR}:/travis \
-        debian:sid /bin/bash -c './debian-setup.sh && ./driver.sh && ccache -s'
+        clangbuiltlinux/ubuntu /bin/bash -c './env-setup.sh && ./driver.sh && ccache -s'
 after_script:
   - sleep 1
 notifications:

driver.sh

@@ -87,7 +87,6 @@ setup_variables() {
 
 check_dependencies() {
   command -v nproc
-  command -v gcc
   command -v "${CROSS_COMPILE:-}"as
   command -v "${CROSS_COMPILE:-}"ld
   command -v ${qemu}

env-setup.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+# Configure our Docker container during Travis builds
+
+# Show all commands and exit upon failure
+set -eux
+
+# By default, Travis's ccache size is around 500MB. We'll
+# start with 2GB just to see how it plays out.
+ccache -M 2G
+
+# Enable compression so that we can have more objects in
+# the cache (9 is most compressed, 6 is default)
+ccache --set-config=compression=true
+ccache --set-config=compression_level=9
+
+# Set the cache directory to /travis/.ccache, which we've
+# bind mounted during 'docker create' so that we can keep
+# this cached across builds
+ccache --set-config=cache_dir=/travis/.ccache
+
+# Clear out the stats so we actually know the cache stats
+ccache -z