[flang][acc] Add missing dependency to bbc tool (llvm#122960)

The LLVM build here:

https://lab.llvm.org/buildbot/#/builders/89/builds/14359/steps/5/logs/stdio
is failing with error:
/usr/bin/ld: tools/flang/tools/bbc/CMakeFiles/bbc.dir/bbc.cpp.o:
undefined reference to symbol
'_ZN3fir3acc25registerOpenACCExtensionsERN4mlir15DialectRegistryE

Add missing dependency.

Author: razvanlupusoru

flang/tools/bbc/CMakeLists.txt

@@ -20,6 +20,7 @@ target_link_libraries(bbc PRIVATE
   CUFDialect
   FIRDialect
   FIRDialectSupport
+  FIROpenACCSupport
   FIRSupport
   FIRTransforms
   FIRBuilder