[flang] fix shared library builds after D136428

https://reviews.llvm.org/D136428 introduced the need for FIRBuilder
library to link against HLFIRDialect to satisfy shared builds.

The PrintFlangFunctionNames failure is unrelated, it is a build
race because many of the headers included in FrontendAction are
tablegen generated. So PrintFlangFunctionNames must wait until its
headers can be safely used. See
https://lab.llvm.org/buildbot/#/builders/191/builds/10340