meson.build: Make radio_tool and objcopy optional

meson.build

@@ -180,11 +180,13 @@ foreach t : targets
 
   if t['flashable']
 
+    if objcopy.found()
       bin = custom_target(name+'_bin',
         output : name+'_bin',
         input : exe,
         command : [objcopy, '-O', 'binary', '@INPUT@', '@OUTPUT@'])
 
+      if radio_tool.found()
         wrap = custom_target(name+'_wrap',
           output : name+'_wrap',
           input : bin,
@@ -199,4 +201,6 @@ foreach t : targets
           output : name+'_flash',
           command : [radio_tool, '-d', '0', '-f', '-i', '@INPUT@'])
       endif
+    endif
+  endif
 endforeach