lit/lit.TestRunner: Add an extra_substitutions argument for executeShTest -- useful for test suites which want to piggyback onto the "shtest" format style.
lit/lit.TestRunner: Add an extra_substitutions argument for executeShTest --
useful for test suites which want to piggyback onto the "shtest" format style.

git-svn-id: a4a6f32337ebd29ad4763b423022f00f68d1c7b7@147684 91177308-0d34-0410-b5e6-96231b3b80d8

lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx