This MR does: - improve startup time when loading a large PDB file (a chromium based PDB file (larger than 4G) now loads in 3,5s) (at the begining of this rewrite, loading the very same PDB file ended with a reboot triggered by the Linux OOM after 30 minutes of heavy swap) - finally untie the new PDB backend for the old one (they are now considered as two independant debug formats, so that we can eventually drop the old one at some point)
-- v2: dbghelp: Let new PDB reader exist independantly of the old one. dbghelp: Rename declarations for old PBD backend. dbghelp: Simplify signature of PDB unwinders. dbghelp: Get fpo stream information directly in new PDB reader. dbghelp: Speed up global symbols at startup.