Clear CCache directory on possible corruption

CCache might segfault on e.g. MacOS which can be resolved by clearing
the cache.
This might be done by deleting the GitHub Actions cache but as there is
one for each build it might become cumbersome.
So delete the folder inside the setup script when `ccache -z`
(simplest command that triggered the segfault) fails.

ci/common_install.sh

@@ -144,6 +144,7 @@ if [ "$B2_USE_CCACHE" == "1" ]; then
         echo
         echo
         B2_USE_CCACHE=0
+        print_on_gha "::error title=CCache::CCache disabled due to an error!"
         set -x
     fi
 fi

ci/setup_ccache.sh

@@ -42,6 +42,12 @@ ccache --version
 # This also sets the default values
 echo "Using cache directory of size ${B2_CCACHE_SIZE:=500M} at '${B2_CCACHE_DIR:=$HOME/.ccache}'"
 
+if ! ccache -z &> /dev/null; then
+  print_on_gha "::warning title=CCache::Possible cache corruption detected!"
+  # Might happen if the cache got corrupted
+  echo "Clearing possibly corrupted CCache directory"
+  rm -rf "$B2_CCACHE_DIR" "$HOME/.ccache"
+fi
 
 ccache --set-config=cache_dir="$B2_CCACHE_DIR"
 ccache --set-config=max_size="$B2_CCACHE_SIZE"