Link-time relaxations of branches are common for MSP430, given that GCC
can generate pessimal branch instructions, and the
-mcode-region=either/-mdata-region=either options to shuffle sections
can further change the type of branch instruction required.

These relaxations can result in invalid code when .uleb128
directives, used in the .gcc_except_table section, are used to calculate
the distance between two labels. A value for the .uleb128 directive is
calculated at assembly-time, and can't be updated at link-time, even if
relaxation causes the distance between the labels to change.

This patch adds relocations for subtract expressions in .uleb128
directives, to allow the linker to re-calculate the value of these
expressions after relaxation has been performed.

Successfully regtested the GCC, G++, Binutils, GAS and LD testsuites
for the msp430-elf target in the default, -mcpu=msp430, -mlarge and
-mlarge/-mdata-region=either/-mcode-region=either configurations.
The patch fixes a number of failures in the G++ testsuite for 
-mlarge/-mdata-region=either/-mcode-region=either.

Ok to apply?

Thanks,
Jozef