clean stale tbb build artifacts before shipping libraries (#255)

Long-lived working trees can carry TBB libraries in
src/tbb/build/lib_release from prior builds -- including from the
pre-6.0 make-based build system, whose Windows DLLs (tbb.dll,
tbbmalloc.dll, tbbmalloc_proxy.dll) could be swept into the installed
package and mask the tbb stub library.

- clear lib_release before repopulating it in useBundledTbb(), so
  installs ship exactly what the current build produced
- enable the (previously commented-out) removal of src/tbb/build in
  cleanup.R; since the cmake migration, the bundled TBB is rebuilt from
  scratch on every install, so these artifacts are not reused anyway

Author: kevinushey

src/install.libs.R

@@ -236,6 +236,10 @@ useBundledTbb <- function() {
       full.names = TRUE
    )
 
+   # clear any artifacts from prior builds, so that we only ship
+   # the libraries produced by the build above
+   unlink("tbb/build/lib_release", recursive = TRUE)
+
    dir.create("tbb/build/lib_release", recursive = TRUE, showWarnings = FALSE)
    file.copy(tbbFiles, "tbb/build/lib_release", overwrite = TRUE)
    unlink("tbb/build-tbb", recursive = TRUE)

tools/config/cleanup.R

@@ -2,8 +2,11 @@
 # Clean up files generated during configuration here.
 # Use 'remove_file()' to remove files generated during configuration.
 
-# unlink("src/tbb/build", recursive = TRUE)
-# unlink("src/tbb/build-tbb", recursive = TRUE)
+# NOTE: stale artifacts in src/tbb/build can otherwise be swept into the
+# installed package; the bundled TBB is rebuilt from scratch on each
+# install, so nothing is lost by removing these
+unlink("src/tbb/build", recursive = TRUE)
+unlink("src/tbb/build-tbb", recursive = TRUE)
 unlink("inst/lib",  recursive = TRUE)
 unlink("inst/libs", recursive = TRUE)
 unlink("inst/include/index.html", recursive = TRUE)