Add support for an additional dictionary in the per-arch plists

that may be embedded in the Contents/Resources subdir of a dSYM
bundle.  These allow for the specification of a build-time path
to debug-time path remapping for source files.  Files may be built
in /BuildDirectory/sources/project-100 but when the debugger is
run, they're actually found via ~sources/project-100 - this plist
allows for that remapping through the DBGBuildSourcePath and
DBGSourcePath keys.

This patch adds support for a new DBGSourcePathRemapping
dictionary in the plist where the keys are the build-time paths
and the values are the debug-time paths that they should be
remapped to.  There are instances were we have multiple possible
build-time paths that need to be included, so the dictionary was
required.

<rdar://problem/26725174> 

llvm-svn: 276729