Fixes #56930 (#57000)

* Don't eliminate store for the following sequence of instructions
```
ldr wzr, [addrReg, #immOff]
str wzr, [addrReg, #immOff]
```

* Add regression test for #56930

src/coreclr/jit/emitarm64.cpp

@@ -15697,7 +15697,11 @@ bool emitter::IsRedundantLdStr(
         // Make sure src and dst registers are not same.
         //  ldr x0, [x0, #4]
         //  str x0, [x0, #4]  <-- can't eliminate because [x0+3] is not same destination as previous source.
-        if ((reg1 != reg2) && (prevReg1 == reg1) && (prevReg2 == reg2) && (imm == prevImm))
+        // Note, however, that we can not eliminate store in the following sequence
+        //  ldr wzr, [x0, #4]
+        //  str wzr, [x0, #4]
+        // since load operation doesn't (and can't) change the value of its destination register.
+        if ((reg1 != reg2) && (prevReg1 == reg1) && (prevReg2 == reg2) && (imm == prevImm) && (reg1 != REG_ZR))
         {
             JITDUMP("\n -- suppressing 'str reg%u [reg%u, #%u]' as previous 'ldr reg%u [reg%u, #%u]' was from same "
                     "location.\n",

src/tests/JIT/Regression/JitBlue/Runtime_56930/Runtime_56930.cs

@@ -0,0 +1,39 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+
+namespace Runtime_56930
+{
+    class C0
+    {
+        public int F1;
+        public C0(int f1)
+        {
+            F1 = f1;
+        }
+    }
+
+    class Program
+    {
+        static C0 s_2 = new C0(1);
+
+        public static int Main()
+        {
+            // Since the following statement is a dead store the next two statements will become
+            // a NULLCHECK(s_2) followed by STOREIND(&s_2[8], 0)
+            int val = s_2.F1;
+            s_2.F1 = 0;
+
+            // On Arm64 these will be compiled to
+            //
+            // ldr wzr, [x0, #8]
+            // str wzr, [x0, #8]
+            //
+            // The issue was that the JIT falsely assumes the store to be redundant and eliminated
+            // the instruction during pipehole optimizations.
+
+            return s_2.F1 + 100;
+        }
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_56930/Runtime_56930.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+  <PropertyGroup>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>