[flang][driver] Add missing dependency in CMake files

[awarzynski]

Summary

The Flang driver depends on libclangBasic. This means, among other
things, that some of the tablegen files (e.g. diagnostic definitions)
need to be generated before various libclangBasic header files can be
included (e.g. DiagnosticIDs.h). If we are lucky, libclangBasic is
indeed built before various flang driver libraries that depend on it
are. This patch makes sure that this is deterministic - i.e.
libclangBasic is built before the Flang driver libraries are.

flang/lib/Frontend/CMakeLists.txt

 add_flang_library(flangFrontend
   CompilerInstance.cpp
   CompilerInvocation.cpp
   FrontendOptions.cpp
 
+  DEPENDS
+  clangBasic
+
   LINK_LIBS
   clangBasic
   clangDriver
   # TODO: Added to re-use clang's TextDiagnosticBuffer & TextDiagnosticPrinter.
   # Add a custom implementation for Flang and remove this dependency.
   clangFrontend
 
   LINK_COMPONENTS
   Option
   Support
 )

flang/lib/FrontendTool/CMakeLists.txt

 add_flang_library(flangFrontendTool
   ExecuteCompilerInvocation.cpp
 
+  DEPENDS
+  clangBasic
+
   LINK_LIBS
   clangBasic
   clangDriver
 
   LINK_COMPONENTS
   Option
   Support
 )