whisper : support GGML_BACKEND_DL (whisper/2843)

* whisper : support GGML_BACKEND_DL

* fix DTW crash

* whisper.objc : fix build - add ggml-cpp.h

---------

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

ggml/src/CMakeLists.txt

@@ -226,6 +226,9 @@ add_library(ggml-base
             gguf.cpp)
 
 target_include_directories(ggml-base PRIVATE .)
+if (GGML_BACKEND_DL)
+    target_compile_definitions(ggml-base PUBLIC GGML_BACKEND_DL)
+endif()
 
 add_library(ggml
             ggml-backend-reg.cpp)