Instead of building the test suites inherited from BoringSSL as
seperate executables, link them all together into one executable,
giving all their `main` functions unique names.
This allows all the tests to be run, even on platforms that don't have
traditional process spawning, and avoids the need to keep track of
directory names even on platforms that do support process spawning.
This also makes it easier to integrate new BoringSSL test suites on
Windows, because we don't need to create a new `vcxproj` file for each
one.
Having one test executable may also make code coverage easier.
A program integrating ring may not necessarily want ring's tests to run
as part of |make check|. Instead, define a rule |check-ring| that can
a Makefile can use as a dependency to run the ring tests, and do that
in ring's Makefile.
Travis CI doesn't have a new enough version of CMake readily available,
and I've been wanting to replace the CMake-based build system for other
reasons. This kills the Windows support, but I'm intending to add a
native msbuild build system for Windows soon. Also, this builds in
OPENSSL_NO_ASM mode for now.
