[flang][unittest] Add a missing dependency

In https://reviews.llvm.org/D103612, a definition of an instance of
`Fortran::parser::AnalyzedObjectsAsFortran` was moved (that object is
used in unparsing). That, in turn, introduced a dependency of the unit
tests on the `FortranEvaluate` library, which defines
`AnalyzedObjectsAsFortran`.

That dependency was missed in D103612 and has caused shared-library
builds to fail. I'm submitting this without a review, as it's rather
straightforward omission.

flang/unittests/Frontend/CMakeLists.txt

@@ -11,4 +11,5 @@ target_link_libraries(FlangFrontendTests
   FortranParser
   FortranSemantics
   FortranCommon
+  FortranEvaluate
 )