Add option for number of threads used by build system (#8346)

* Add option for number of threads used by build system

Attempt to fix https://github.com/armbian/build/issues/6907

* Add CPUTHREADS to replace USEALLTHREADS

Defaults to 150% as was always the case, otherwise allow user to override number of threads.

lib/functions/configuration/compilation-config.sh

@@ -24,10 +24,15 @@ function prepare_compilation_vars() {
 	# moved from config: this does not belong in configuration. it's a compilation thing.
 	# optimize build time with 100% CPU usage
 	CPUS=$(grep -c 'processor' /proc/cpuinfo)
-	if [[ $USEALLCORES != no ]]; then
-		CTHREADS="-j$((CPUS + CPUS / 2))"
-	else
-		CTHREADS="-j1"
+
+	# Default to 150% of CPUs to maximize compilation speed
+	CTHREADS="-j$((CPUS + CPUS / 2))"
+
+	# If CPUTHREADS is defined and a valid positive integer allow user to override CTHREADS
+	# This is useful for limiting Armbian build to a specific number of threads, e.g. for build servers
+	if [[ "$CPUTHREADS" =~ ^[1-9][0-9]*$ ]]; then
+    	CTHREADS="-j$CPUTHREADS"
+		echo "Using user-defined thread count: $CTHREADS"
 	fi
 
 	call_extension_method "post_determine_cthreads" "config_post_determine_cthreads" <<- 'POST_DETERMINE_CTHREADS'

lib/functions/configuration/main-config.sh

@@ -95,8 +95,6 @@ function do_main_configuration() {
 		TZDATA="Etc/UTC" # If not /etc/timezone at host, default to UTC.
 	fi
 
-	USEALLCORES=yes # Use all CPU cores for compiling
-
 	[[ -z $EXIT_PATCHING_ERROR ]] && EXIT_PATCHING_ERROR="" # exit patching if failed
 	[[ -z $HOST ]] && HOST="$BOARD"
 	cd "${SRC}" || exit