We have two sources for path remapping information that we get out

of a dSYM per-uuid plist that may be present (dsymutil does not
create this plist, it is only added after the fact by additional
tools) -- either the DBGBuildSourcePath + DBGSourcePath pair of
k-v entries which give us the build-time and debug-time remapping,
or the newer DBGSourcePathRemapping dictionary which may give us
multiple remappings.

I'm changing the order that we process these & add them to the
list of source remappings.  If the DBGSourcePathRemapping dict
is present, it should be the first entries we will try.

<rdar://problem/36481989> 

llvm-svn: 322418