Fix condition flags reuse optimization

[mikedn]

This optimization is not valid for unsigned LT/LE/GT/GE relops. Using the Carry flag this way indicates that the operation overflowed, not that the result is less than 0, that's impossible for unsigned integers.

Fixes #14321

[mikedn]

jit-diff summary:

Total bytes of diff: 345 (0.00% of base)
    diff is a regression.
Total byte diff includes 0 bytes from reconciling methods
        Base had    0 unique methods,        0 unique bytes
        Diff had    0 unique methods,        0 unique bytes
Top file regressions by size (bytes):
         133 : System.Private.CoreLib.dasm (0.00% of base)
         116 : System.Text.RegularExpressions.dasm (0.12% of base)
          27 : Microsoft.CSharp.dasm (0.01% of base)
          13 : Microsoft.CodeAnalysis.CSharp.dasm (0.00% of base)
          12 : System.Collections.Concurrent.dasm (0.02% of base)
14 total files with size differences (0 improved, 14 regressed), 65 unchanged.
Top method regessions by size (bytes):
          38 : System.Private.CoreLib.dasm - GenericArraySortHelper`1:PickPivotAndPartition(ref,int,int):int (18 methods)
          22 : System.Text.RegularExpressions.dasm - RegexParser:ScanCharClass(bool,bool):ref:this
          20 : System.Private.CoreLib.dasm - GenericArraySortHelper`1:DownHeap(ref,int,int,int) (18 methods)
          18 : System.Text.RegularExpressions.dasm - RegexParser:ScanGroupOpen():ref:this
          15 : System.Private.CoreLib.dasm - GenericArraySortHelper`1:SwapIfGreaterWithItems(ref,int,int) (18 methods)
Top method improvements by size (bytes):
          -1 : System.Private.CoreLib.dasm - Task:FinishSlow(bool):this
          -1 : System.Private.CoreLib.dasm - Task:ProcessChildCompletion(ref):this
          -1 : System.Private.CoreLib.dasm - Task:WaitAllBlockingCore(ref,int,struct):bool
          -1 : System.Private.CoreLib.dasm - SetOnCountdownMres:Invoke(ref):this
          -1 : System.Private.CoreLib.dasm - WhenAllPromise:Invoke(ref):this
88 total methods with size differences (8 improved, 80 regressed), 66464 unchanged.

So we're back where we were before #14027.

[BruceForstall]

@dotnet/jit-contrib

[jkotas]

@dotnet/jit-contrib I am merging this because of it is fixing corefx test break. If you have any feedback it can be addressed in follow up PR.