Add semaphores syscalls

[yunwei37]

Add semaphores syscalls

• add semaphore in linux-object::sync
• add semary in linux-object::ipc
• add semget syscall
• add semop syscall
• add semctl syscall
• tests
  • libc-test may fail because of Segmentation fault cause by fork
  • modify from libc-test but use vfork instead
• documents

other

• move time related structs to linux-object::time

[coveralls]

Pull Request Test Coverage Report for Build 213275357

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 180 of 283 (63.6%) changed or added relevant lines in 10 files are covered.
• 19 unchanged lines in 4 files lost coverage.
• Overall coverage increased (+0.6%) to 46.961%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
linux-object/src/error.rs	0	1	0.0%
linux-object/src/process.rs	10	13	76.92%
linux-object/src/ipc/semary.rs	37	48	77.08%
linux-object/src/ipc/mod.rs	19	37	51.35%
linux-syscall/src/ipc.rs	49	69	71.01%
linux-object/src/sync/semaphore.rs	43	64	67.19%
linux-object/src/time.rs	16	45	35.56%

Files with Coverage Reduction	New Missed Lines	%
../../../../../usr/share/rust/.cargo/registry/src/git.luolix.top-1ecc6299db9ec823/bitflags-1.2.1/src/lib.rs	1	41.82%
linux-syscall/src/lib.rs	3	46.36%
linux-object/src/signal/action.rs	4	28.13%
linux-object/src/signal/mod.rs	11	7.5%

Totals
Change from base Build 210967384:	0.6%
Covered Lines:	6752
Relevant Lines:	14378

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💛 - Coveralls