Use Ninja for BoringSSL if available

[ilammy]

Ninja build tool significantly reduces compilation time for BoringSSL in default configuration.

This is mostly due to the fact that it performs parallel builds by default but there are other gains (Makefiles that CMake generates are not that optimal). make -j4 is also a viable option, but it often ends up brittle.

Timings for my machine

As you can see, there is some gain in wall clock time (real), resulting in shorter builds. However, this comes mostly from better parallelization if you look at the user time.

time make ENGINE=boringssl

master:

real	4m30.623s
user	3m32.624s
sys	0m33.530s

with ninja:

real	2m47.085s
user	4m47.580s
sys	0m34.020s

time emmake make wasmthemis

master:

real	2m59.856s
user	2m14.338s
sys	0m29.650s

with ninja:

real	1m57.756s
user	3m13.189s
sys	0m33.403s

Timings for GitHub Actions

It's always nice to see builds run a bit quicker.

master:

Test set	Job	Step	Time
Themis Core	Unit tests (ubuntu)	Build Themis Core (BoringSSL)	3m 09s
Themis Core	Unit tests (macos)	Build Themis Core (BoringSSL)	6m 57s
Themis Core	Memory leaks	Build Themis Core	4m 22s
WasmThemis	Unit tests (16.x)	Build WasmThemis	2m 34s

with ninja:

Test set	Job	Step	Time
Themis Core	Unit tests (ubuntu)	Build Themis Core (BoringSSL)	2m 33s
Themis Core	Unit tests (macos)	Build Themis Core (BoringSSL)	2m 26s
Themis Core	Memory leaks	Build Themis Core	2m 48s
WasmThemis	Unit tests (16.x)	Build WasmThemis	1m 45s

Checklist

• Change is covered by automated tests
• Benchmark results are attached (if applicable)
• The coding guidelines are followed
• Public API has proper documentation
• Changelog is updated