perf: use ccache and parallel make, and skip already-built newer-R candidates in bulk (#240)

.crow/build-all-versions.yaml

@@ -140,6 +140,7 @@ steps:
       - ${ARCH}-binaries-r-dep-cache-${OS}-${OS_VERSION//./}:/mnt/cache
     commands:
       - git clone -q https://pat-s:$$REPO_RO_TOKEN@git.devxy.io/devxy/build-cran-binaries.git .
+      - . local/compiler-cache.sh
       - mkdir -p /mnt/cache/uvr/cache /mnt/cache/uvr/packages /mnt/cache/R-pkgs /mnt/cache/ccache /mnt/cache/packages
       # The primary pass must not rely on build-all-versions-install-deps having
       # run on *this* agent: depends_on only orders the steps, but the cache