use standard NETCOREAPP3_1_OR_GREATER directive

Directory.Build.props

@@ -33,8 +33,4 @@
   <PropertyGroup Condition="$(Configuration.StartsWith('Release')) == true">
     <Optimize>true</Optimize>
   </PropertyGroup>
-
-  <PropertyGroup>
-    <DefineConstants Condition="$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)','netcoreapp3.1'))">$(DefineConstants);NETCORE31COMPATIBLE</DefineConstants>
-  </PropertyGroup>
 </Project>

src/ImageSharp/Memory/Allocators/Internals/Gen2GcCallback.cs

@@ -3,7 +3,7 @@
 
 // Port of BCL internal utility:
 // https://github.com/dotnet/runtime/blob/57bfe474518ab5b7cfe6bf7424a79ce3af9d6657/src/libraries/System.Private.CoreLib/src/System/Gen2GcCallback.cs
-#if NETCORE31COMPATIBLE
+#if NETCOREAPP3_1_OR_GREATER
 using System;
 using System.Runtime.ConstrainedExecution;
 using System.Runtime.InteropServices;

src/ImageSharp/Memory/Allocators/Internals/UniformUnmanagedMemoryPool.cs

@@ -42,7 +42,7 @@ namespace SixLabors.ImageSharp.Memory.Internals
             if (trimSettings.Enabled)
             {
                 UpdateTimer(trimSettings, this);
-#if NETCORE31COMPATIBLE
+#if NETCOREAPP3_1_OR_GREATER || NETFRAMEWORK
                 Gen2GcCallback.Register(s => ((UniformUnmanagedMemoryPool)s).Trim(), this);
 #endif
                 this.lastTrimTimestamp = Stopwatch.ElapsedMilliseconds;
@@ -328,7 +328,7 @@ namespace SixLabors.ImageSharp.Memory.Internals
 
         private bool IsHighMemoryPressure()
         {
-#if NETCORE31COMPATIBLE
+#if NETCOREAPP3_1_OR_GREATER
             GCMemoryInfo memoryInfo = GC.GetGCMemoryInfo();
             return memoryInfo.MemoryLoadBytes >= memoryInfo.HighMemoryLoadThresholdBytes * this.trimSettings.HighPressureThresholdRate;
 #else

src/ImageSharp/Memory/Allocators/UniformUnmanagedMemoryPoolMemoryAllocator.cs

@@ -146,7 +146,7 @@ namespace SixLabors.ImageSharp.Memory
 
         private static long GetDefaultMaxPoolSizeBytes()
         {
-#if NETCORE31COMPATIBLE
+#if NETCOREAPP3_1_OR_GREATER
             // On 64 bit .NET Core 3.1+, set the pool size to a portion of the total available memory.
             // There is a bug in GC.GetGCMemoryInfo() on .NET 5 + 32 bit, making TotalAvailableMemoryBytes unreliable:
             // https://github.com/dotnet/runtime/issues/55126#issuecomment-876779327

tests/ImageSharp.Tests/ImageSharp.Tests.csproj

@@ -7,7 +7,6 @@
     <Platforms>AnyCPU;x64;x86</Platforms>
     <RootNamespace>SixLabors.ImageSharp.Tests</RootNamespace>
     <Configurations>Debug;Release;Debug-InnerLoop;Release-InnerLoop</Configurations>
-    <DefineConstants Condition="$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)','netcoreapp3.1'))">$(DefineConstants);NETCORE31COMPATIBLE</DefineConstants>
   </PropertyGroup>
 
   <Choose>

tests/ImageSharp.Tests/Memory/Allocators/UniformUnmanagedMemoryPoolTests.Trim.cs

@@ -90,7 +90,7 @@ namespace SixLabors.ImageSharp.Tests.Memory.Allocators
                 }
             }
 
-#if NETCORE31COMPATIBLE
+#if NETCOREAPP3_1_OR_GREATER
             public static readonly bool Is32BitProcess = !Environment.Is64BitProcess;
             private static readonly List<byte[]> PressureArrays = new();