command_util: Output array members with backslashes.

command_util: Output array members with backslashes.

This makes sure that the generated code for the definition of the
command array has backslashes at the end of each line.  Currently
this does not matter because make_array_member() is only called when
generating C code where new lines don't matter.

However, ending each line with a backslash allows to use the same
output for a cpp #define which can go into the header file.