ARC: gcc - fixes for improperly calculated jump/branch offsets

Symptoms usually seen are like that:
--->---
Error: operand out of range (128 is not between -128 and 127)
--->---
where range may differ.

Since compiler tries to use jump/branch instructions with the shortest encoding
of offset it's important to calculate required offset properly.

In case of miscalculation by compiler later assembler throws an error because of
inability to encode requested value.

Fixes are taken from current development branch of GCC for ARC and will be a
part of the next release of ARC tools, so at that point patch should be dropped.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Anton Kolesov <akolesov@synopsys.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>