This patch adds epilogue handling capabilities to the DWARF2 unwind
information emission. It also contains tweaks to the x86/x86-64
backend to smooth out the generation of such information.
Background: here at Rice, we have developed a low-overhead callstack
profiler for optimized code that can also record edge count information
at low cost (see our ICS'05 paper for details). The basic idea is to
take callstack samples at timer interrupts; massaging the return address
at sample times ensures that the amount of unwinding is small and
provides edge count data as a bonus.