[Offload] Add OFFLOAD_INCLUDE_TESTS (#143388)

This is a cmake variable which, if set to `OFF` will disable building of
tests. It defaults to the value of `LLVM_INCLUDE_TESTS`.

offload/CMakeLists.txt

@@ -41,6 +41,8 @@ endif()
 
 set(LLVM_COMMON_CMAKE_UTILS ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
 
+option(OFFLOAD_INCLUDE_TESTS "Generate and build offload tests." ${LLVM_INCLUDE_TESTS})
+
 # Add path for custom modules
 list(INSERT CMAKE_MODULE_PATH 0
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
@@ -376,6 +378,7 @@ add_subdirectory(libomptarget)
 add_subdirectory(liboffload)
 
 # Add tests.
+if(OFFLOAD_INCLUDE_TESTS)
   add_subdirectory(test)
 
   # Add unit tests if GMock/GTest is present
@@ -388,3 +391,4 @@ endif()
   if(TARGET llvm_gtest)
     add_subdirectory(unittests)
   endif()
+endif()