Use underscore for prebuilt var

cmake/AwsPrebuildDependency.cmake

@@ -7,7 +7,7 @@
 #  SOURCE_DIR Path to the project.
 #  CMAKE_ARGUMENTS Additional arguments that will be passed to cmake command.
 #
-# Set ${DEPENDENCY_NAME}-PREBUILT variable on success.
+# Set ${DEPENDENCY_NAME}_PREBUILT variable on success.
 function(prebuild_dependency)
     set(oneValueArgs DEPENDENCY_NAME SOURCE_DIR)
     set(multiValueArgs CMAKE_ARGUMENTS)
@@ -62,7 +62,7 @@ function(prebuild_dependency)
     list(INSERT CMAKE_PREFIX_PATH 0 ${depInstallDir}/)
     set(CMAKE_PREFIX_PATH ${CMAKE_PREFIX_PATH} PARENT_SCOPE)
 
-    set(${AWS_PREBUILD_DEPENDENCY_NAME}-PREBUILT TRUE CACHE INTERNAL "Indicate that dependency is built and can be used")
+    set(${AWS_PREBUILD_DEPENDENCY_NAME}_PREBUILT TRUE CACHE INTERNAL "Indicate that dependency is built and can be used")
 
     # Generates installation rules for the dependency project.
     # On installing targets, CMake will just copy this prebuilt version to a designated installation directory.