Clang supports symbol rewrites via the -frewrite-map-file flag,
this patch adds complementary functionality in lldb.
Re-written symbols are required when, for example, two versions of the
same library are linked to the same binary, and the user needs to
differentiate the symbols.
The SymbolRewriter implemented in this patch will use a rewrite map
provided via the 'target symbols rewrite' command to lookup the original
symbol names instead of the names re-written by clang.