Don't download ARM Gnu toolchain if present (#5005)

* check for downloaded toolkit

* rm if not

* force

* this might work better

* don't move, just link

* don't need glob

* try

* try correct path

* check file to prevent error

* fix quotes so globs work

* using an executable which contains version stamp

* docs etc

* fix path

* back to globs we go

* maybe the path is right this time

firmware/provide_gcc.sh

@@ -6,6 +6,9 @@ set -e
 
 # URL to download original toolchain from
 URL="https://github.com/rusefi/build_support/raw/master/rusefi-arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi.tar.xz"
+# This is the md5sum of the /bin/arm-none-eabi-ld executable within the archive, used for verifying we have the proper version.
+# If you change the above URL, you will need to update this checksum as well.
+MANIFEST_SUM="8e50ee1adb41acfd56fc38d74d6bb18e"
 # colloquial directory name, to afford re-use of script
 COLLOQUIAL="gcc-arm-none-eabi"
 # temporary working directory
@@ -13,22 +16,23 @@ TMP_DIR="/tmp/rusefi-provide_gcc"
 
 archive="${URL##*/}"
 
-# Cleanup prior [failed] runs
-rm -rf "${TMP_DIR}"
+SWD="$PWD"
 
-# Download and extract archive
-echo Downloading and extracting ${archive}
-mkdir -p "${TMP_DIR}"
-cd "${TMP_DIR}"
-curl -L -o "${archive}" "${URL}"
-tar -xaf "${archive}"
-rm "${archive}"
+# If the checksum file doesn't exist, or if its checksum doesn't match, then download and install the archive.
+if [ ! -f "${TMP_DIR}"/*/bin/arm-none-eabi-ld ] ||\
+   [ "$MANIFEST_SUM" != "$(md5sum ${TMP_DIR}/*/bin/arm-none-eabi-ld | cut -d ' ' -f 1)" ]; then
+	rm -rf "${TMP_DIR}"
+	# Download and extract archive
+	echo Downloading and extracting ${archive}
+	mkdir -p "${TMP_DIR}"
+	cd "${TMP_DIR}"
+	curl -L -o "${archive}" "${URL}"
+	tar -xaf "${archive}"
+	rm "${archive}"
+else
+	echo "Toolkit already present"
+fi
 
 # Create colloquially named link
-archive_dir="$(echo *)"
-cd - >/dev/null
-mv "${TMP_DIR}/${archive_dir}" "$(pwd)"
-ln -s "${archive_dir%/}" "${COLLOQUIAL}"
-
-# Delete downloaded archive
-rm -rf "${TMP_DIR}"
+cd "$SWD"
+ln -s "${TMP_DIR}"/* "${COLLOQUIAL}"