-) Adding question marks to important tools so they can be overriden from environment variables.
 -) Removing all traces of -ldl since BoringSSL doesn't implement OpenSSL's DSO and doesn't require it.

Importantly:
- allows matching timeout values between makefile and run_tests without
  repeating ourselves
- allows borrowing of compiler flags by other build systems

There's still a little too much build configuration built into our
Makefile, but we can start attacking that over time.

Somehow these are getting loaded at bad addresses by whatever kernels we have on our Jenkins slaves. Fix the load address to something safe to avoid this.