Compilation fixes for MSVC

This makes a few changes to compile the libary under clang-cl targeting
windows 10.

- We cannot cast a path to std::string in msvc
- Incorrect function names for generated code, causing linker failures
  under windows.

Bug: 186568522
Test: Can successfully build packet gen as part of android emulator
Change-Id: I0edebc3bf459669998295dfbee08df30d4381ff8