optimize scanning of vulkan shader files in ncnn_add_layer() (#6019)

Author: maxint

cmake/ncnn_add_layer.cmake

@@ -130,8 +130,8 @@ macro(ncnn_add_layer class)
         set(layer_declaration "${layer_declaration}#include \"layer/vulkan/${name}_vulkan.h\"\n")
         set(layer_declaration "${layer_declaration}namespace ncnn { DEFINE_LAYER_CREATOR(${class}_vulkan) }\n")
 
-        file(GLOB_RECURSE NCNN_SHADER_SRCS "layer/vulkan/shader/${name}.comp")
-        file(GLOB_RECURSE NCNN_SHADER_SUBSRCS "layer/vulkan/shader/${name}_*.comp")
+        file(GLOB NCNN_SHADER_SRCS "layer/vulkan/shader/${name}.comp")
+        file(GLOB NCNN_SHADER_SUBSRCS "layer/vulkan/shader/${name}_*.comp")
         list(APPEND NCNN_SHADER_SRCS ${NCNN_SHADER_SUBSRCS})
         foreach(NCNN_SHADER_SRC ${NCNN_SHADER_SRCS})
             ncnn_add_shader(${NCNN_SHADER_SRC})