Meta: Expect sync-local.sh script at repository root

This used to be in Kernel/, next to the build-root-filesystem.sh script,
which was then moved to Meta/ during the transition to CMake but has the
working directory set to Build/, effectively expecting it there - which
seems silly.

TL;DR: Very confusing. Use an explicit path relative to SERENITY_ROOT
instead and update the .gitignore files.

.gitignore

@@ -40,3 +40,4 @@ compile_commands.json
 Ports/packages.db
 .idea/
 cmake-build-debug/
+sync-local.sh

Kernel/.gitignore

@@ -1,4 +1,3 @@
 kernel.map
-sync-local.sh
 *.pcap
 eth_null*

Meta/build-root-filesystem.sh

@@ -125,7 +125,22 @@ ln -s checksum mnt/bin/sha256sum
 ln -s checksum mnt/bin/sha512sum
 echo "done"
 
+if [ -f "${SERENITY_ROOT}/Kernel/sync-local.sh" ] || [ -f "${SERENITY_ROOT}/Build/sync-local.sh" ]; then
+ # TODO: Deprecated on 2021-01-30. In a few months, remove this 'if'.
+ tput setaf 1
+ echo
+ echo " +-----------------------------------------------------------------------------+"
+ echo " | |"
+ echo " | WARNING: sync-local.sh, previously located in Kernel/ and later Build/ |"
+ echo " | must be moved to \$SERENITY_ROOT! |"
+ echo " | See https://github.com/SerenityOS/serenity/pull/5172 for details. |"
+ echo " | |"
+ echo " +-----------------------------------------------------------------------------+"
+ echo
+ tput sgr 0
+fi
+
 # Run local sync script, if it exists
-if [ -f sync-local.sh ]; then
- sh sync-local.sh
+if [ -f "$SERENITY_ROOT}/sync-local.sh" ]; then
+ sh "${SERENITY_ROOT}/sync-local.sh"
 fi