[NativeAOT-LLVM] Work around poor inlined memset code quality in LLVM

[SingleAccretion]

See llvm/llvm-project#79692.

The diffs are a bit mixed, but still overall significantly positive. The regressions are due to the use of the "opaque" add pattern to form non-wrapping offset additions, something we can remove in favor of the new nusw GEP feature once we update to the next EMSDK.

Diffs (WasmDebugging):

Summary of Code Size diffs:
(Lower is better)

Total bytes of base: 647680
Total bytes of diff: 646552
Total bytes of delta: -1128 (-0.17% % of base)
Average relative delta: -1.12%
    diff is an improvement
    average relative diff is an improvement

Top method regressions (percentages):
          21 ( 4.65% of base) : 1079.dasm - S_P_CoreLib_System_Text_EncoderExceptionFallbackBuffer__Fallback_0
           7 ( 3.08% of base) : 1126.dasm - S_P_CoreLib_System_Number__TryFormatFloat<Double__Char>
           7 ( 3.08% of base) : 1137.dasm - S_P_CoreLib_System_Number__TryFormatFloat<Single__Char>
           4 ( 2.74% of base) : 1081.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_NativeFormat_NativeFormatRuntimeNamedTypeInfo__get_Name
           7 ( 2.48% of base) : 1080.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_RuntimeNamedTypeInfo__get_FullName
          42 ( 2.10% of base) : 1190.dasm - S_P_Reflection_Execution_Internal_Reflection_Execution_NativeFormatEnumInfo__GetEnumValuesAndNames
           4 ( 1.68% of base) : 1200.dasm - S_P_CoreLib_System_GC___AllocateUninitializedArray_g__AllocateNewUninitializedArray_52_0<Char>
           4 ( 1.68% of base) : 1139.dasm - S_P_CoreLib_System_GC___AllocateUninitializedArray_g__AllocateNewUninitializedArray_52_0<Bool>
          12 ( 1.07% of base) : 1173.dasm - S_P_CoreLib_System_Reflection_Runtime_General_NativeFormatMetadataReaderExtensions__IsCustomAttributeOfType
           4 ( 1.04% of base) : 1116.dasm - S_P_CoreLib_System_Collections_Generic_KeyValuePair__PairToString
           6 ( 0.95% of base) : 1084.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_NativeFormat_NativeFormatRuntimeNamedTypeInfo__ToString
           4 ( 0.82% of base) : 1175.dasm - S_P_TypeLoader_Internal_Metadata_NativeFormat_MetadataTypeHashingAlgorithms__ComputeHashCode
           2 ( 0.79% of base) : 1220.dasm - S_P_CoreLib_System_Buffers_ProbabilisticMapState__FindModulus
          10 ( 0.75% of base) : 1101.dasm - S_P_StackTraceMetadata_Internal_StackTraceMetadata_MethodNameFormatter__EmitMethodParameters_0
           7 ( 0.72% of base) : 1151.dasm - S_P_CoreLib_System_Reflection_Runtime_General_NamespaceChain___ctor
           4 ( 0.54% of base) : 1165.dasm - S_P_CoreLib_System_CrashInfo__WriteHeader
           2 ( 0.53% of base) : 1171.dasm - S_P_CoreLib_System_Collections_Generic_ArraySortHelper_2<System___Canon__System___Canon>__HeapSort
           5 ( 0.47% of base) : 1182.dasm - S_P_CoreLib_System_Reflection_AssemblyNameFormatter__AppendQuoted
           7 ( 0.45% of base) : 1181.dasm - S_P_TypeLoader_Internal_Runtime_TypeLoader_TypeLoaderEnvironment__TryGetStaticGenericMethodComponents
           2 ( 0.23% of base) : 1205.dasm - S_P_CoreLib_System_Collections_Generic_ArraySortHelper_2<System___Canon__System___Canon>__IntroSort

Top method improvements (percentages):
         -48 (-8.50% of base) : 1217.dasm - S_P_CoreLib_System_SpanHelpers__ClearWithoutReferences
         -12 (-7.79% of base) : 1034.dasm - S_P_StackTraceMetadata_Internal_StackTraceMetadata_MethodNameFormatter__EmitTypeInstantiationName
         -21 (-6.38% of base) : 1038.dasm - S_P_StackTraceMetadata_Internal_StackTraceMetadata_MethodNameFormatter__EmitArrayTypeName
         -15 (-4.24% of base) : 1059.dasm - S_P_CoreLib_System_Reflection_Runtime_General_NativeFormatMetadataReaderExtensions__GetAttributeTypeHandle
         -17 (-4.15% of base) : 1162.dasm - S_P_CoreLib_System_Buffers_ProbabilisticWithAsciiCharSearchValues_1<S_P_CoreLib_System_Buffers_IndexOfAnyAsciiSearcher_Default>___ctor
         -10 (-4.05% of base) : 1037.dasm - S_P_StackTraceMetadata_Internal_StackTraceMetadata_MethodNameFormatter_SigTypeContext__GetHandleAt
          -6 (-3.92% of base) : 1166.dasm - S_P_CoreLib_System_CrashInfo__WriteIntValue
         -13 (-3.81% of base) : 1224.dasm - S_P_CoreLib_System_Number__FormatFloat<Double>
          -3 (-3.80% of base) : 1061.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_RuntimeFunctionPointerTypeInfo__GetHashCode
          -3 (-3.80% of base) : 1237.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_RuntimeConstructedGenericTypeInfo__GetHashCode
         -13 (-3.64% of base) : 1136.dasm - S_P_CoreLib_System_Number__FormatFloat<Single>
          -5 (-3.27% of base) : 1078.dasm - S_P_CoreLib_System_Text_EncoderExceptionFallbackBuffer__Fallback
          -5 (-3.23% of base) : 1167.dasm - S_P_CoreLib_System_ArgumentOutOfRangeException__ThrowNegativeOrZero<Int32>
          -5 (-3.23% of base) : 1141.dasm - S_P_CoreLib_System_ArgumentOutOfRangeException__ThrowNegative<Int32>
         -15 (-3.21% of base) : 1015.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_RuntimeTypeInfo_TypeComponentsCache__CreatePerNameQueryCaches
          -3 (-3.16% of base) : 1202.dasm - String__Format_1
          -8 (-2.87% of base) : 1184.dasm - S_P_CoreLib_System_CrashInfo__WriteHexValue
          -8 (-2.87% of base) : 1186.dasm - S_P_CoreLib_System_CrashInfo__WriteHexValue_0
          -6 (-2.79% of base) : 1209.dasm - S_P_CoreLib_System_GC__GetGCMemoryInfo_0
          -5 (-2.70% of base) : 1164.dasm - S_P_CoreLib_System_ArgumentOutOfRangeException__ThrowLess<Int32>

239 total methods with Code Size differences (216 improved, 23 regressed)

[SingleAccretion]

@dotnet/nativeaot-llvm

[yowl]

LGTM, thanks!

[jkotas]

Thanks!