Re-use prologue parsing code that was already written instead of having two...

Re-use prologue parsing code that was already written instead of having two copies of code that parse line table prologues.

Also since we always read in the DWARF data or mmap it, we don't need to make a copy of the strings for the directories and file names, we can just store "cosnt char *" values. Every place that uses the prologues use them temporarily and then throw them away so no one is expecting the directory and filename strings to live longer than the parse functions.

llvm-svn: 251310