Allow parallel jobs to be passed to V8 build

e.g. JOBS=2 make

Makefile

@@ -1,4 +1,5 @@
-WAF=python tools/waf-light --jobs=1
+JOBS?=1 # The number of parallel processes. Use 'JOBS=2 make' for more.
+WAF=python tools/waf-light --jobs=$(JOBS)
 
 all:
 	@$(WAF) build

wscript

@@ -235,9 +235,10 @@ def v8_cmd(bld, variant):
   else:
     mode = "debug"
 
-  cmd_R = 'python "%s" -C "%s" -Y "%s" visibility=default mode=%s %s library=static snapshot=on'
+  cmd_R = 'python "%s" -j %d -C "%s" -Y "%s" visibility=default mode=%s %s library=static snapshot=on'
 
   cmd = cmd_R % ( scons
+                , Options.options.jobs
                 , bld.srcnode.abspath(bld.env_of_name(variant))
                 , v8dir_src
                 , mode
@@ -276,6 +277,7 @@ def build_v8(bld):
 def build(bld):
   print "DEST_OS: " + bld.env['DEST_OS']
   print "DEST_CPU: " + bld.env['DEST_CPU']
+  print "Parallel Jobs: " + str(Options.options.jobs)
 
   if not bld.env["USE_SYSTEM"]:
     bld.add_subdirs('deps/libeio deps/libev deps/c-ares')