When running `SymInitializeW(GetCurrentProcess(), NULL, TRUE)` in a 32-bit EXE on 64-bit macOS, there are a number of syscall faults resulting from 64-bit pointers being truncated to 32 bits and then passed to `ReadProcessMemory()`. Fix these, mostly by widening variables to 64 bits.
-- v2: dbghelp: Don't try to load 64-bit ELF/Mach-O debug info in a Wow64 process.