ARC: Adjustments for gcc 4.8

* DWARF unwinder related
  + Force DWARF2 compliant .debug_frame (gcc 4.8 defaults to DWARF4
    which kernel unwinder can't grok).
  + Discard the additional .eh_frame generated
  + Discard the dwarf4 debug info generated by -gdwarf-2 for normal
    no debug case

* 4.8 already uses arc600 multilibs for -mno-mpy

* switch to using uclibc compiler (to get -mmedium-calls and -mno-sdata)
  and also since buildroot can only use 1 toolchain

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>