[stdlib] add overflow checks for some pointer arithmetic

[glessard]

• Pointer arithmetic uses operations that can overflow.
• This adds overflow checks added for recent additions to pointer arithmetic (rounding and property pointers).
• The basic advanced(by:) functions will be dealt with separately.

[glessard]

@swift-ci please benchmark

[glessard]

As expected, these changes have no real effect on current benchmarks:

Performance (x86_64): -O

Regression	OLD	NEW	DELTA	RATIO
FlattenListLoop	1001	1623	+62.1%	0.62x (?)

Code size: -O

Performance (x86_64): -Osize

Regression	OLD	NEW	DELTA	RATIO
FlattenListFlatMap	3020	4350	+44.0%	0.69x (?)
Improvement	OLD	NEW	DELTA	RATIO
SequenceAlgosRange	2390	2170	-9.2%	1.10x (?)
SequenceAlgosArray	2400	2180	-9.2%	1.10x (?)
DictionaryKeysContainsCocoa	15	14	-6.7%	1.07x (?)

Code size: -Osize

Performance (x86_64): -Onone

Code size: -swiftlibs

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 mini
  Model Identifier: Macmini8,1
  Processor Name: 6-Core Intel Core i7
  Processor Speed: 3.2 GHz
  Number of Processors: 1
  Total Number of Cores: 6
  L2 Cache (per Core): 256 KB
  L3 Cache: 12 MB
  Memory: 32 GB

[glessard]

@swift-ci please test

[glessard]

@swift-ci please test

[Catfish-Man]

Looks good to me, I appreciate the thorough tests