rsynth: only build and test rsynth-say

dlookup depends on gdbm and we don't have that.
Also disabled SCA tests for say.
added regression test for the machine call graph

LLVM commit [33d842c Update IR when merging slots in stack coloring] fixed an
issue that would break our analysis information on UNKNOWN (ptr) calls, this
test tries to assert that based on the exported PML.