Revert "Merge libm to libc"

 - We have all-in-one mode in near future!

This reverts commit cbe417526f3b51f23537d623c4030636d9aef715.
Config: Add all-in-one mode

 - libdl, libc,libm and dynamic linker all integrated into olibc.so in all-in-one mode.
 - Code size about ~380k.

 Modification in all-in-one mode
  - Drop libdl info in dynamic linker, instead look up from olibc.so and export
    dl* functions.
  - Keep soinfo for dynamic linker (olibc.so) for futher symbol look-up.
  - Drop malloc/calloc/free/calloc stubs in dynamic linker since it's all-in-one
    and include whole libc, so we need self-discipline to don't call those functions
    in dynmic linker part now.