This patch adds an option -j to sim build so that one can use parallel make without having to hard-code -j X in the machine definition file (or using mdbkey).

• sim-build: add option to specify number of make jobs

  this adds an option --jobs (or -j) to sim build that controls how many make jobs are used by setting a replacement for @MAKEJOBS@ the default is 1

• simopts: fix handling of default values for non-boolean options