updating makefile dependencies to correctly update stanc through a generated c++ file
Merge pull request #1178 from stan-dev/feature/issue-1108-makefile-stanc

Updated makefile dependencies for auto-generated cpp files
Fixes #1108
Merge branch 'develop' of https://github.com/stan-dev/stan into bugfix/issue-1177-keyword-var
fix #1177, allow variables with prefixes matching keywords