Add compile-only tests verifying headers are self-contained

[mloskot]

Add Boost.Jam rule generating test target for each header found in specified location.
List test suites (target aliases) for groups of headers.
Build self_contained_headers test only if CI environment variable is NOT defined or on-demand, if TEST_HEADERS environment variable is defined, or if b2 test/self_contained_headers is requested from command line.

Related to issue #523

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First, this PR does not attempt to fix any headers, not yet.

I've run all the headers tests on 24 CPUs (48 logical cores) as follows:

cd libs/geometry
b2 -j 16 test/self_contained_headers >build.log 2>&1

AFAICT, it compile-tests ~900 headers in less than 4 minutes:

cat build.log | grep -E -o "c\+\+.+\~hpp\.test" | sort | uniq | wc -l
898
cat build.log | grep -E -o "passed.+~hpp\.test" | wc -l
547
cat build.log | grep -E -o "failed.+~hpp\.test" | wc -l
350

And, I have only included several extensions, see alias-es and comments in test/self_contained_headers/Jamfile.

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To run the tests on CI services, it should be enough to define environment variable TEST_HEADERS=1 for one just build job. For example, Boost.GIL defines it for first job only https://travis-ci.org/boostorg/gil/jobs/447353675

[vissarion]

Thanks, this is useful.

[mloskot]

Thanks!

[awulkiew]

Wow, thanks! Just to be sure, does it work with CircleCI? (EDIT: And by "it" I mean bjam properly defining CI env ;)).

[mloskot]

I see no reason why it should not work on CircleCI - I mean, those tests should be automatically filtered there as on Travis or AppVeyor.

CircleCI does define CI as built-in environment variable and b2 just reads the environment variables (no CI needs to be defined in any Jamfile).

[awulkiew]

Ok, thanks for the explanation.

[awulkiew]

@mloskot This change polluted our regression matrix (https://www.boost.org/development/tests/develop/developer/geometry.html). I'm considering disabling it by default. Or maybe do you have some other ideas?

EDIT: Furthermore on windows the generated paths are too long even with --abbreviate-paths

[mloskot]

@awulkiew I'm trying to make those tests on-demand only in #529

I'm not sure how to avoid the long paths. Since the .cpp file is generated, I assumed that is not an issue, so ignored it.

[awulkiew]

If they are not run by default it is no longer an issue since we can just run them on linux. Thanks!