Update file comment to contain a bunch of the overview mapping-info
  documentation previously buried within the file.
 Remove some unnecessary include/using stmts.
 Rename pass to MappingInfoCollector.
 Rewrite a lot of it so it doesn't use global instance variables and so
  it outputs into MappingInfo objects and then dumps those out, instead of going
  straight to an assembly file.
 Change name of factory to getMappingInfoCollector.
 Fold prologue & epilogue writers into MappingInfo methods.

lib/Target/Sparc/FInfo.cpp:
 Correct file comment to reflect above change

lib/Target/Sparc/Sparc.cpp:
 Change name of factory to getMappingInfoCollector.

llvm-svn: 6617