This patch creates a cache of file lists in line tables referenced by
type units. This cache is used to avoid parsing a line table twice
(since a file list will generally be shared by many type units).
It also sets things up in a way that parsing of DW_AT_decl_file
attributes will keep working even when we stop creating lldb compile
units for dwarf type units, but it stops short of actually doing that.
This means that the request for files now go directly to SymbolFileDWARF
instead of being routed there indirectly via the
As a result of this, a number of occurences of SymbolContext variables
in DWARFASTParserClang have become unused, so I remove them.
This patch reduces the number of times a file list is being parsed, but
the situation is still suboptimal, as the parsed list is being copied
multiple times. This will be fixed when we stop creating CompileUnits
for DWARF type units.