Reapply my previous asmprinter changes now with more testing and two

additional bug fixes:

1. The bug that everyone hit was a problem in the asmprinter where it
   would remove $stub but keep the L prefix on a name when emitting the
   indirect symbol.  This is easy to fix by keeping the name of the stub
   and the name of the symbol in a StringMap instead of just keeping a
   StringSet and trying to reconstruct it late.

2. There was a problem printing the personality function.  The current
   logic to print out the personality function from the DWARF information
   is a bit of a cesspool right now that duplicates a bunch of other 
   logic in the asm printer.  The short version of it is that it depends
   on emitting both the L and _ prefix for symbols (at least on darwin)
   and until I can untangle it, it is best to switch the mangler back to
   emitting both prefixes.

llvm-svn: 75646