build: avoid ggml-qnn backend breaking other backend's builds

Author: zhouwg

ggml/CMakeLists.txt

@@ -188,7 +188,7 @@ option(GGML_OPENCL                          "ggml: use OpenCL"
 option(GGML_OPENCL_PROFILING                "ggml: use OpenCL profiling (increases overhead)" OFF)
 option(GGML_OPENCL_EMBED_KERNELS            "ggml: embed kernels"                             ON)
 option(GGML_OPENCL_USE_ADRENO_KERNELS       "ggml: use optimized kernels for Adreno"          ON)
-option(GGML_QNN                             "ggml: use QNN"                                   ON)
+option(GGML_QNN                             "ggml: use QNN"                                   OFF)
 
 # toolchain for vulkan-shaders-gen
 set   (GGML_VULKAN_SHADERS_GEN_TOOLCHAIN "" CACHE FILEPATH "ggml: toolchain file for vulkan-shaders-gen")

ggml/src/ggml-qnn/CMakeLists.txt

@@ -4,9 +4,6 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Android")
     find_library(LOG_LIB log)
     set(QNN_LINK_LIBRARIES ${LOG_LIB})
     set(QNN_DEFAULT_LIB_SEARCH_PATH "/data/local/tmp/" CACHE STRING "customized library search path for QNN backend")
-else()
-    message(FATAL_ERROR "QNN now only available on Android")
-endif()
 
 if(NOT DEFINED GGML_QNN_SDK_PATH)
     # try read from environment variable
@@ -31,3 +28,7 @@ target_link_libraries(ggml-qnn PRIVATE ${QNN_LINK_LIBRARIES})
 
 string(REGEX REPLACE "/$" "" GGML_QNN_DEFAULT_LIB_SEARCH_PATH "${QNN_DEFAULT_LIB_SEARCH_PATH}")
 target_compile_definitions(ggml-qnn PRIVATE GGML_QNN_DEFAULT_LIB_SEARCH_PATH="${QNN_DEFAULT_LIB_SEARCH_PATH}/")
+
+else()
+    message(FATAL_ERROR "QNN now only available on Android")
+endif()