fbt: added support for FBT_NO_SYNC environment variable to skip submodule update at start (#1363)

fbt

@@ -5,12 +5,13 @@ set -e
 SCRIPTDIR="$( dirname -- "$0"; )";
 SCONS_EP=${SCRIPTDIR}/lib/scons/scripts/scons.py
 
-if [[ -d .git ]]; then
-    git submodule update --init
-else # Not in a git repo
-    echo Not in a git repo, please clone with git clone --recursive
-    # Return error code 1 to indicate failure
-    exit 1
+if [[ -z "${FBT_NO_SYNC:-}" ]] ; then
+    if [[ -d .git ]]; then
+        git submodule update --init
+    else
+        echo Not in a git repo, please clone with git clone --recursive
+        exit 1
+    fi
 fi
 
 SCONS_DEFAULT_FLAGS="-Q --warn=target-not-built"