Recent changes to the way registers are handled broke reporting of AVX
registers (i.e. YMMx). This change restores the functionality by:
- concatenating the higher half of the YMMx registers to their
corresponding XMMx lower half (YMMx registers do not have an
independent DWARF register number)
- modifying the formatSSEReg function to handle them when they are
present.
Fixes#2033
5a5d5f9e68