Default build menu jobs to CPU count

contrib/agrarian-build-menu.sh

@@ -3,7 +3,6 @@ set -euo pipefail
 
 REPO_URL="${REPO_URL:-https://github.com/pacificao/agrarian.git}"
 WORKDIR="${WORKDIR:-$HOME/agrarian}"
-JOBS="${JOBS:-1}"
 HOST_WIN64="${HOST_WIN64:-x86_64-w64-mingw32}"
 
 MENU_CHOICE=""
@@ -21,6 +20,18 @@ if [[ -z "${BRANCH:-}" ]]; then
 fi
 BRANCH="${BRANCH:-main}"
 
+detect_build_jobs() {
+  if command -v nproc >/dev/null 2>&1; then
+    nproc
+  elif command -v getconf >/dev/null 2>&1; then
+    getconf _NPROCESSORS_ONLN
+  else
+    echo 1
+  fi
+}
+
+JOBS="${JOBS:-$(detect_build_jobs)}"
+
 if [[ "${EUID:-$(id -u)}" -eq 0 && "${ALLOW_ROOT_BUILD_MENU:-0}" != "1" ]]; then
   cat >&2 <<EOF
 Do not run this script with sudo.

doc/build-menu.md

@@ -50,7 +50,7 @@ The script can be configured with environment variables:
     REPO_URL=https://github.com/pacificao/agrarian.git
     BRANCH=<current checkout branch, or main when run standalone>
     WORKDIR=$HOME/agrarian
-    JOBS=1
+    JOBS=<detected CPU count>
 
 Example: