cc and flex: read JIT_CC_FLAGS, use tcc where available.

..because tcc compiles twice as fast.
go: read JIT_GO_FLAGS
bugfix
optimizations

a) don’t spawn echo in a child process
b) don’t test for dist files when dist compilation is not supported
add test for flags.

Well, technically this is a test for CFLAGs only.
Adds .gitignore file for tests