[X86] Remove IntrArgMemOnly from ldmxcsr intrinsic.

Since we're leaving this as ReadWrite with the "write" reflecting
the update to MXCSR, we shouldn't say it only writes arg memory.

Hopefully this fixes the issue reported in post-commit in D93571.

llvm/include/llvm/IR/IntrinsicsX86.td

@@ -286,7 +286,7 @@ let TargetPrefix = "x86" in {  // All intrinsics start with "llvm.x86.".
                          // FIXME: LDMXCSR does not actually write to memory,
                          // but intrinsic properties are generated incorrectly
                          // for IntrReadMem+IntrHasSideEffects.
-                        [/*IntrReadMem,*/ IntrArgMemOnly, IntrHasSideEffects]>;
+                        [/*IntrReadMem, IntrArgMemOnly,*/ IntrHasSideEffects]>;
 }
 
 // Misc.