document configure.win

configure.win

@@ -1,10 +1,18 @@
 
+# On R 4.3 and 4.4, Abseil can be resolved using pkg-config. Otherwise,
+# build a copy of Abseil-cpp using CMake.
 if pkg-config absl_base --libs 2>/dev/null; then
   echo "Using Abseil from RTools via pkg-config"
 else
+  # Build the libraries
   WIN_CPPFLAGS="-DABSL_FORCE_WAITER_MODE=4" tools/build_absl.sh
+
+  # Remove the build directory (its existence causes a check warning on R 4.2)
+  rm -rf tools/build
 fi
 
+# On R 4.3 and 4.4, OpenSSL can be resolved using pkg-config. Otherwise,
+# Use rwinlibs to download a static library for that toolchain.
 if pkg-config openssl --libs 2>/dev/null; then
   echo "Using openssl from RTools via pkg-config"
 else