ci: Address tight disk space on GHA runners (#4974)

- Mount the host's root under /host/root so it's visible in the
containers.
- Remove stuff we don't need to free lots of disk space.
- While we're at it, arrange for the commands (copied from OSL) that
allow the containers to see a CPU, when available.

This is freeing 20+ GB!

---------

Signed-off-by: Larry Gritz <[email protected]>

Author: lgritz

.github/workflows/build-steps.yml

@@ -95,6 +95,10 @@ jobs:
     container:
       image: ${{ inputs.container }}
       volumes: ${{ fromJson( inputs.container_volumes ) }}
+      options: -v /:/host/root ${{ (contains(inputs.runner, 'gpu') && '-e NVIDIA_DRIVER_CAPABILITIES=compute,graphics,utility --gpus all') || '-e A=x' }}
+      # Extra options:
+      # - Ensure the GPU runners have OptiX is visible in the container.
+      # - Mount the native filesystem under /host/root
     env:
       CXX: ${{inputs.cxx_compiler}}
       CC: ${{inputs.cc_compiler}}

src/build-scripts/gh-installdeps.bash

@@ -7,7 +7,14 @@
 
 
 set -ex
-df -h
+
+# Make extra space on the runners
+df -h .
+time rm -rf /usr/local/lib/android /host/root/usr/local/lib/android &
+sleep 3
+# rather than block, delete in background, but give it a few secs to start
+# clearing things out before moving on.
+# Other candidates, if we need it: /usr/share/dotnet /usr/local/.ghcup
 
 
 #
@@ -219,7 +226,8 @@ if [[ "$USE_ICC" != "" ]] ; then
     export CC=icc
 fi
 
-df -h
+df -h .
+df -h /host/root || true
 
 # Save the env for use by other stages
 src/build-scripts/save-env.bash