ARC: dw2 unwind: don't force dwarf 2

In .debug_frame based unwinding regime, we used to force -gdwarf-2 since
kernel unwinder only claimed to handle dwarf 2. This changed since commit
6d0d5060 ("ARC: dw2 unwind: Don't bail for CIE.version != 1")
which added some support beyond dwarf 2, atleast to handle CIE != 1

The ill-effect of -gdwarf-2 is that it forces generation of .debug_*
sections, which bloats loadable modules .ko files. For the curious, this
doesn't affect vmlinx binary since linker script discards .debug_* but
same discard is not yet implemented for modules.

So it seems we can drop the -gdwarf-2 toggle, which should not be needed
anyways given that we now use .eh_frame based unwinding.

I've verified using GNU 2016.09-engo10 that the actual unwind info is
not different with or w/o this toggle - but the debug_* sections are
gone for good.

before
-----
arc-linux-readelf -S q_proc.ko-unwinding-1-eh_frame-switch | grep debug
  [15] .debug_info       PROGBITS        00000000 000300 00d08d 00 	0   0  1
  [16] .rela.debug_info  RELA            00000000 0162a0 008844 0c   I 29  15  4
  [17] .debug_abbrev     PROGBITS        00000000 00d38d 0005f8 00 	0   0  1
  [18] .debug_loc        PROGBITS        00000000 00d985 000070 00 	0   0  1
  [19] .rela.debug_loc   RELA            00000000 01eae4 0000c0 0c   I 29  18  4
  [20] .debug_aranges    PROGBITS        00000000 00d9f5 000040 00 	0   0  1
  [21] .rela.debug_arang RELA            00000000 01eba4 000030 0c   I 29  20  4
  [22] .debug_ranges     PROGBITS        00000000 00da35 000018 00 	0   0  1
  [23] .rela.debug_range RELA            00000000 01ebd4 000030 0c   I 29  22  4
  [24] .debug_line       PROGBITS        00000000 00da4d 000b5b 00 	0   0  1
  [25] .rela.debug_line  RELA            00000000 01ec04 0000cc 0c   I 29  24  4
  [26] .debug_str        PROGBITS        00000000 00e5a8 007831 01   MS 0   0  1

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

arch/arc/Makefile

@@ -47,7 +47,6 @@ endif
 
 upto_gcc44    :=  $(call cc-ifversion, -le, 0404, y)
 atleast_gcc44 :=  $(call cc-ifversion, -ge, 0404, y)
-atleast_gcc48 :=  $(call cc-ifversion, -ge, 0408, y)
 
 cflags-$(atleast_gcc44)			+= -fsection-anchors
 
@@ -68,11 +67,6 @@ endif
 
 cflags-$(CONFIG_ARC_DW2_UNWIND)		+= -fasynchronous-unwind-tables
 
-# By default gcc 4.8 generates dwarf4 which kernel unwinder can't grok
-ifeq ($(atleast_gcc48),y)
-cflags-$(CONFIG_ARC_DW2_UNWIND)		+= -gdwarf-2
-endif
-
 ifndef CONFIG_CC_OPTIMIZE_FOR_SIZE
 # Generic build system uses -O2, we want -O3
 # Note: No need to add to cflags-y as that happens anyways