modutils-24: use xasprintf and xzalloc where appropriate,

modutils-24: use xasprintf and xzalloc where appropriate,
 remove unreachanble code
build system: correct some dependencies in config system
init: convert one #if into if() - for Rob.

function                                             old     new   delta
obj_string_patch                                     136     129      -7
bb_init_module_24                                   4759    4615    -144
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(add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-151)           Total: -151 bytes