fix: build for any kind of arm combination

* This simplification allows to use src/CMakeLists.txt directly
  within a project that has its own toolchain.
* factorize arm and x86 cmake code
* Introduce NCNN_CMAKE_VERBOSE option to reduce cmake verbosity

CMakeLists.txt

@@ -28,6 +28,7 @@ option(NCNN_OPENCV "minimal opencv structure emulation" OFF)
 option(NCNN_BENCHMARK "print benchmark information for every layer" OFF)
 option(NCNN_PIXEL "convert and resize from/to image pixel" ON)
 option(NCNN_PIXEL_ROTATE "rotate image pixel orientation" OFF)
+option(NCNN_CMAKE_VERBOSE "print verbose cmake messages" OFF)
 
 if(NCNN_OPENMP)
     find_package(OpenMP)

src/CMakeLists.txt

@@ -31,44 +31,37 @@ macro(ncnn_add_layer class)
         option(WITH_LAYER_${name} "build with layer ${name}" ON)
     endif()
 
-    message("WITH_LAYER_${name} = ${WITH_LAYER_${name}}")
+    if(NCNN_CMAKE_VERBOSE)
+        message(STATUS "WITH_LAYER_${name} = ${WITH_LAYER_${name}}")
+    endif()
 
     if(WITH_LAYER_${name})
         list(APPEND ncnn_SRCS "${CMAKE_CURRENT_SOURCE_DIR}/layer/${name}.cpp")
 
         # look for arch specific implementation and append source
         # optimized implementation for armv7 aarch64
-        if((ANDROID AND ("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "armv7-a"))
-            OR (ANDROID AND ("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "aarch64"))
-            OR (UNIX AND ("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "armv7l"))
-            OR (UNIX AND ("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "aarch64"))
-            OR (IOS AND ("${CMAKE_OSX_ARCHITECTURES}" STREQUAL "armv7"))
-            OR (IOS AND ("${CMAKE_OSX_ARCHITECTURES}" STREQUAL "arm64"))
-            OR (IOS AND ("${CMAKE_OSX_ARCHITECTURES}" STREQUAL "armv7;arm64")))
-            if(EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/layer/arm/${name}_arm.cpp")
-                list(APPEND ncnn_SRCS "${CMAKE_CURRENT_SOURCE_DIR}/layer/arm/${name}_arm.cpp")
-                set(WITH_LAYER_${name}_arm 1)
-            endif()
+        if(CMAKE_SYSTEM_PROCESSOR MATCHES "^(arm|aarch64)")
+            set(arch arm)
         else()
-            if(EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/layer/x86/${name}_x86.cpp")
-                list(APPEND ncnn_SRCS "${CMAKE_CURRENT_SOURCE_DIR}/layer/x86/${name}_x86.cpp")
-                set(WITH_LAYER_${name}_x86 1)
+            set(arch x86)
+        endif()
+        set(LAYER_SRC ${CMAKE_CURRENT_SOURCE_DIR}/layer/${arch}/${name}_${arch}.cpp)
+        if(EXISTS ${LAYER_SRC})
+            set(WITH_LAYER_${name}_${arch} 1)
+            list(APPEND ncnn_SRCS ${LAYER_SRC})
+            if(NCNN_CMAKE_VERBOSE)
+                message(STATUS "Adding layer: ${LAYER_SRC}")
             endif()
         endif()
     endif()
 
     # generate layer_declaration and layer_registry file
     if(WITH_LAYER_${name})
-        if(WITH_LAYER_${name}_arm)
-            file(APPEND ${CMAKE_CURRENT_BINARY_DIR}/layer_declaration.h
-                "extern Layer* ${class}_arm_layer_creator();\n")
-            file(APPEND ${CMAKE_CURRENT_BINARY_DIR}/layer_registry.h
-                "#if NCNN_STRING\n{\"${class}\",${class}_arm_layer_creator},\n#else\n{${class}_arm_layer_creator},\n#endif\n")
-        elseif(WITH_LAYER_${name}_x86)
+        if(WITH_LAYER_${name}_${arch})
             file(APPEND ${CMAKE_CURRENT_BINARY_DIR}/layer_declaration.h
-                "extern Layer* ${class}_x86_layer_creator();\n")
+                "extern Layer* ${class}_${arch}_layer_creator();\n")
             file(APPEND ${CMAKE_CURRENT_BINARY_DIR}/layer_registry.h
-                "#if NCNN_STRING\n{\"${class}\",${class}_x86_layer_creator},\n#else\n{${class}_x86_layer_creator},\n#endif\n")
+                "#if NCNN_STRING\n{\"${class}\",${class}_${arch}_layer_creator},\n#else\n{${class}_${arch}_layer_creator},\n#endif\n")
         else()
             file(APPEND ${CMAKE_CURRENT_BINARY_DIR}/layer_declaration.h
                 "extern Layer* ${class}_layer_creator();\n")