[benchmark] Use Int.random instead of arc4random_uniform.

[drodriguez]

This should be more portable, and easier to understand to Swift
programmers that the BSD function.

The usage of the BSD function was breaking the Android CI (https://ci-external.swift.org/job/oss-swift-RA-linux-ubuntu-16.04-android-arm64/448/ and https://ci-external.swift.org/job/oss-swift-RA-linux-ubuntu-16.04-android/2247/). The CI machines have libbsd-devel, but I don’t understand why arc4random_uniform is not being found. I decided for this faster workaround, which makes the code more “swifty”, while I figure out what's happening in the CI machines.

[compnerd]

libbsd is not used

[compnerd]

@swift-ci please benchmark

[swift-ci]

Performance: -Osize

TEST	OLD	NEW	DELTA	RATIO
Improvement
ObjectiveCBridgeStubNSDateRefAccess	400	371	-7.2%	1.08x (?)

How to read the data

The tables contain differences in performance which are larger than 8% and differences in code size which are larger than 1%.

If you see any unexpected regressions, you should consider fixing the
regressions before you merge the PR.

Noise: Sometimes the performance results (not code size!) contain false
alarms. Unexpected regressions which are marked with '(?)' are probably noise.
If you see regressions which you cannot explain you can try to run the
benchmarks again. If regressions still show up, please consult with the
performance team (@eeckstein).

Hardware Overview

  Model Name: Mac Pro
  Model Identifier: MacPro6,1
  Processor Name: 12-Core Intel Xeon E5
  Processor Speed: 2.7 GHz
  Number of Processors: 1
  Total Number of Cores: 12
  L2 Cache (per Core): 256 KB
  L3 Cache: 30 MB
  Memory: 64 GB

[drodriguez]

Even if the original commit was reverted in #24093, I think the improvement should be considered if the commit is tried to be land again.

[rajbarik]

Hi! @drodriguez! Are you waiting on me here? The changes look fine to me. Please commit. Thanks.

[drodriguez]

@rajbarik: since the other one was reverted, i cannot apply this one. Maybe you just need to resubmit, and incorporate this piece in your version. That's what Slava seems to imply in #24065.

[palimondo]

I believe this change has incorporated into #24206, so this one can he closed.