GH-50208: [CI][C++][Python] Disable ccache hash_dir

Author: pitrou

ci/scripts/ccache_setup.sh

@@ -19,10 +19,12 @@
 
 set -eux
 
+# See similar definitions in compose.yaml under the `x-ccache` key
 {
   echo "ARROW_USE_CCACHE=ON"
   echo "CCACHE_COMPILERCHECK=content"
   echo "CCACHE_COMPRESS=1"
   echo "CCACHE_COMPRESSLEVEL=6"
   echo "CCACHE_MAXSIZE=1G"
+  echo "CCACHE_NOHASHDIR=1"
 } >> "$GITHUB_ENV"

compose.yaml

@@ -59,6 +59,9 @@ x-ccache: &ccache
   CCACHE_COMPRESSLEVEL: 6
   CCACHE_MAXSIZE: 1G
   CCACHE_DIR: /ccache
+  # Some builds (such as PyArrow) copy their source files in a temporary directory,
+  # avoid hashing the current directory to make ccache useful on those builds.
+  CCACHE_NOHASHDIR: 1
 
 x-common: &common
   GITHUB_ACTIONS: