Consider statically linking wslbridge-backend

[rprichard]

wslbridge-backend is currently distributed as a dynamic executable, which makes it dependent on the libc it's built against (most recently, glibc in the Ubuntu 14.04 WSL image). To use wslbridge with a non-glibc WSL distribution, it's necessary to rebuild wslbridge-backend. If it were instead distributed as a static binary, maybe that wouldn't be necessary.

Current issues with static linking:

• The new call to getpwuid (for Invoke user's default shell #17) generates a linker warning:

  wslbridge-backend.cc:(.text.startup+0x116f): warning: Using 'getpwuid' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
  

  Maybe wslbridge could parse /etc/passwd or invoke getent passwd "$USER" if things like LDAP and NIS are relevant.

• Linking with -static -pthread produces a binary that mostly works, but apparently attempting to join a thread causes a segfault. The fix is to build with -static -pthread -Wl,--whole-archive -lpthread -Wl,--no-whole-archive: https://stackoverflow.com/a/45271521

[Biswa96]

That is only a warning. g++ can compile the binary. But that also depends on /etc/passwd file. What happens if that file is not present? WSL team has added a feature in init where Linux distributions can be run without /etc/passwd. See this: microsoft/WSL#3001