tools: limit parallelism with ninja in V8 builds

If `JOBS` has been set in the environment to limit build parallelism,
pass that onto `ninja` when building V8.

tools/make-v8.sh

@@ -9,6 +9,11 @@ cd deps/v8 || exit
 find . -type d -name .git -print0 | xargs -0 rm -rf
 ../../tools/v8/fetch_deps.py .
 
+JOBS_ARG=
+if [ "$JOBS" != "" ]; then
+  JOBS_ARG="-j $JOBS"
+fi
+
 ARCH=$(arch)
 if [ "$ARCH" = "s390x" ] || [ "$ARCH" = "ppc64le" ]; then
   TARGET_ARCH=$ARCH
@@ -46,10 +51,10 @@ if [ "$ARCH" = "s390x" ] || [ "$ARCH" = "ppc64le" ]; then
   gcc --version
   export PKG_CONFIG_PATH=$BUILD_TOOLS/pkg-config
   gn gen -v "out.gn/$BUILD_ARCH_TYPE" --args="is_component_build=false is_debug=false use_goma=false goma_dir=\"None\" use_custom_libcxx=false v8_target_cpu=\"$TARGET_ARCH\" target_cpu=\"$TARGET_ARCH\" v8_enable_backtrace=true $CC_WRAPPER"
-  ninja -v -C "out.gn/$BUILD_ARCH_TYPE" d8 cctest inspector-test
+  ninja -v -C "out.gn/$BUILD_ARCH_TYPE" "${JOBS_ARG}" d8 cctest inspector-test
 else
   DEPOT_TOOLS_DIR="$(cd _depot_tools && pwd)"
   # shellcheck disable=SC2086
   PATH="$DEPOT_TOOLS_DIR":$PATH tools/dev/v8gen.py "$BUILD_ARCH_TYPE" --no-goma $V8_BUILD_OPTIONS
-  PATH="$DEPOT_TOOLS_DIR":$PATH ninja -C "out.gn/$BUILD_ARCH_TYPE/" d8 cctest inspector-test
+  PATH="$DEPOT_TOOLS_DIR":$PATH ninja -C "out.gn/$BUILD_ARCH_TYPE/" "${JOBS_ARG}" d8 cctest inspector-test
 fi