Fix build: rename GetLastError to avoid Win32 collision, fix strprintf varargs

- Rename CTorProcess::GetLastError() and CTorEmbedded::GetLastError() to
  GetStartupError() so they don't shadow the Win32 GetLastError() API,
  which caused a std::string-to-DWORD conversion error on Windows.
- Qualify the one Win32 call as ::GetLastError() for clarity.
- Pass torError.c_str() to strprintf instead of std::string, fixing
  Clang's -Wnon-pod-varargs error on macOS.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/tor/tor_process.cpp

@@ -314,7 +314,7 @@ bool CTorProcess::Start(const std::string& dataDir, int socks, int hsPort, bool
             NULL, NULL,
             &si, &pi))
     {
-        DWORD err = GetLastError();
+        DWORD err = ::GetLastError();
         lastError = strprintf("CreateProcess failed for Tor binary '%s' with Windows error %lu", torBinaryPath.c_str(), err);
         printf("ERROR: Failed to start Tor process (error %lu)\n", err);
         return false;