Enable use of the Arduino core cache, stashing our cached prebuilt cores in /tmp

Signed-off-by: Jesse Vincent <jesse@keyboard.io>

bin/kaleidoscope-builder

@@ -24,11 +24,14 @@ build_version () {
     LIB_PROPERTIES_PATH="${LIB_PROPERTIES_PATH:-"../.."}"
     LIB_VERSION="$(cd "$(find_sketch)"; (grep version= "${LIB_PROPERTIES_PATH}/library.properties" 2>/dev/null || echo version=0.0.0) | cut -d= -f2)${GIT_VERSION}"
 }
-build_paths() {
 
+build_paths() {
     BUILD_PATH="${BUILD_PATH:-"$(mktemp -d 2>/dev/null || mktemp -d -t 'build')"}"
     OUTPUT_DIR="${OUTPUT_DIR:-output/${LIBRARY}}"
     OUTPUT_PATH="${OUTPUT_PATH:-${SOURCEDIR}/${OUTPUT_DIR}}"
+    STABLE_TEMP_DIR="${STABLE_TEMP_DIR:-/tmp/kaleidoscope-${USER}}"
+    CORE_CACHE_PATH="${CORE_CACHE_PATH:-${STABLE_TEMP_DIR}/arduino-cores}"
+    mkdir -p "$CORE_CACHE_PATH"
 }
 
 build_filenames () {
@@ -236,6 +239,7 @@ compile () {
 	      -libraries "${BOARD_HARDWARE_PATH}/.." \
         ${local_LIBS} \
 	      ${EXTRA_BUILDER_ARGS} \
+	      -build-cache "${CORE_CACHE_PATH}" \
 	      -build-path "${BUILD_PATH}" \
 	      -ide-version "${ARDUINO_IDE_VERSION}" \
 	      -prefs "compiler.cpp.extra_flags=-std=c++11 -Woverloaded-virtual -Wno-unused-parameter -Wno-unused-variable -Wno-ignored-qualifiers ${ARDUINO_CFLAGS} ${LOCAL_CFLAGS}" \