[flang] Fix build when examples are disabled

Without this change I get a build error due to the missing Bye target
when I configure my build with -DLLVM_INCLUDE_EXAMPLES=OFF.
This check for LLVM_BUILD_EXAMPLES matches the checks in llvm and lld.

Reviewed By: mgorny

Pull Request: llvm#137908

Author: arichardson

flang/test/CMakeLists.txt

@@ -82,7 +82,7 @@ if (FLANG_INCLUDE_RUNTIME)
   list(APPEND FLANG_TEST_DEPENDS flang_rt.runtime)
 endif ()
 
-if (LLVM_ENABLE_PLUGINS AND NOT WIN32 AND NOT FLANG_STANDALONE_BUILD)
+if (LLVM_BUILD_EXAMPLES AND LLVM_ENABLE_PLUGINS AND NOT WIN32 AND NOT FLANG_STANDALONE_BUILD)
   list(APPEND FLANG_TEST_DEPENDS Bye)
 endif()