Fix RegexCompiler regression on 32-bit for some set matching

src/libraries/System.Text.RegularExpressions/gen/RegexGenerator.Emitter.cs

@@ -4331,6 +4331,10 @@ private static string MatchCharacterClass(RegexOptions options, string chExpr, s
             // Next, handle sets where the high - low + 1 range is <= 64.  In that case, we can emit
             // a branchless lookup in a ulong that does not rely on loading any objects (e.g. the string-based
             // lookup we use later).  This nicely handles common sets like [0-9A-Fa-f], [0-9a-f], [A-Za-z], etc.
+            // Note that unlike RegexCompiler, the source generator doesn't know whether the code is going to be
+            // run in a 32-bit or 64-bit process: in a 64-bit process, this is an optimization, but in a 32-bit process,
+            // it's a deoptimization.  In general we optimize for 64-bit perf, so this code remains; it complicates
+            // the code too much to try to include both this and a fallback for the check.
             if (analysis.OnlyRanges && (analysis.UpperBoundExclusiveIfOnlyRanges - analysis.LowerBoundInclusiveIfOnlyRanges) <= 64)
             {
                 additionalDeclarations.Add("ulong charMinusLow;");

src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexCompiler.cs

@@ -5203,7 +5203,9 @@ private void EmitMatchCharacterClass(string charClass)
             // Next, handle sets where the high - low + 1 range is <= 64.  In that case, we can emit
             // a branchless lookup in a ulong that does not rely on loading any objects (e.g. the string-based
             // lookup we use later).  This nicely handles common sets like [0-9A-Fa-f], [0-9a-f], [A-Za-z], etc.
-            if (analysis.OnlyRanges && (analysis.UpperBoundExclusiveIfOnlyRanges - analysis.LowerBoundInclusiveIfOnlyRanges) <= 64)
+            // We skip this on 32-bit, as otherwise using 64-bit numbers in this manner is a deoptimization
+            // when compared to the subsequent fallbacks.
+            if (IntPtr.Size == 8 && analysis.OnlyRanges && (analysis.UpperBoundExclusiveIfOnlyRanges - analysis.LowerBoundInclusiveIfOnlyRanges) <= 64)
             {
                 // Create the 64-bit value with 1s at indices corresponding to every character in the set,
                 // where the bit is computed to be the char value minus the lower bound starting from