IRGen: Value witness functions don't need shared linkage

[slavapestov]

No description provided.

[slavapestov]

Let's just make sure I didn't screw up code size...

[slavapestov]

@swift-ci Please benchmark

[slavapestov]

@swift-ci Please smoke test

[rjmccall]

Sure. It's easy to promote back to shared if we ever want to do something that would make use of this.

[swift-ci]

Build comment file:

Performance: -O

TEST	OLD	NEW	DELTA	RATIO
Improvement
IterateData	1535	1298	-15.4%	1.18x

Performance: -Osize

TEST	OLD	NEW	DELTA	RATIO
Regression
DictionaryBridgeToObjC_Access	827	998	+20.7%	0.83x
Improvement
IterateData	1387	1219	-12.1%	1.14x
UTF8Decode_InitFromData_ascii	672	591	-12.1%	1.14x

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: 8-Core Intel Xeon E5
  Processor Speed: 3 GHz
  Number of Processors: 1
  Total Number of Cores: 8
  L2 Cache (per Core): 256 KB
  L3 Cache: 25 MB
  Memory: 16 GB

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