Revert "Add possibility to ask for libbenchmark version number (#1004)"

[dmah42]

Reverts #1403

due to two reported bugs:

version status has nothing useful (not a git checkout) and
#1416

[dmah42]

@Matthdonau sorry for reverting your work. feel free to revert the revert and make the improvements necessary to make this work:

1. instead of exiting when we don't get a git version, we should return the default (l74-ish of the python script).
2. figure out why cmake embedding fails... maybe we don't export the version.h correctly?

[Matthdonau]

Regarding 1: I think I don't understand. What you describe is what should happen. if no git is available or we are not in a git checkout the default project version (currently 1.6.1) is used.
Regarding 2: @dominichamon I suspect the problem is that the version.h header is generated in CMAKE_BINARY_DIR while PROJECT_BINARY_DIR would be correct

[dmah42]

Regarding 1: I think I don't understand. What you describe is what should happen. if no git is available or we are not in a git checkout the default project version (currently 1.6.1) is used.

l71 .. we exit. we don't return the default. this is being tickled when using snapshot zip releases I think.

Regarding 2: @dominichamon I suspect the problem is that the version.h header is generated in CMAKE_BINARY_DIR while PROJECT_BINARY_DIR would be correct

ah maybe. we should do whatever the other generated header is doing as that seems to work.

[Matthdonau]

I made a PR. The problem is: If there is no volatile-status.txt there is no default version to default to. Is this really the issue here or is it the issue I fixed in the PR? If not I'll guess we could move the definition of the default version to the BUILD.bazel file. If the result of the problem was that libbbenchmark reported DEFAULT_VERSION as version it is the bug fixed in the PR I guess