[GR-51179] Provide a method to set the physical memory size.

PullRequest: graal/16497

Author: christianhaeubl

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/heap/PhysicalMemory.java

@@ -63,6 +63,12 @@ public static boolean isInitializationInProgress() {
         return LOCK.isHeldByCurrentThread();
     }
 
+    @Uninterruptible(reason = "May only be called during early startup.")
+    public static void setSize(UnsignedWord value) {
+        VMError.guarantee(!isInitialized(), "PhysicalMemorySize must not be initialized yet.");
+        cachedSize = value;
+    }
+
     /**
      * Returns the size of physical memory in bytes, querying it from the OS if it has not been
      * initialized yet.