Don't repeat default for CMAKE_CXX_FLAGS_DEBUG

Debug build type already has defaults, and the flags we set are likely to be those defaults on Unix-like platforms. Why break Windows compatibility?

ghstack-source-id: 83c3214
ghstack-comment-id: 2599288517
Pull Request resolved: pytorch/executorch#7743

Author: swolchok

CMakeLists.txt

@@ -164,8 +164,6 @@ else()
   set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -O2")
 endif()
 
-set(CMAKE_CXX_FLAGS_DEBUG "-O0 -g")
-
 option(EXECUTORCH_BUILD_ANDROID_JNI "Build Android JNI" OFF)
 
 option(EXECUTORCH_BUILD_ARM_BAREMETAL