Make JNA calls optional

The introduction of max number of processes and max size virtual memory
checks inadvertently made JNA non-optional on OS X and Linux. This
commit wraps these calls in a check to see if JNA is available so that
JNA remains optional.

Closes #17492

core/src/main/java/org/elasticsearch/bootstrap/Bootstrap.java

@@ -133,9 +133,8 @@ final class Bootstrap {
             // we've already logged this.
         }
 
-        JNANatives.trySetMaxNumberOfThreads();
-
-        JNANatives.trySetMaxSizeVirtualMemory();
+        Natives.trySetMaxNumberOfThreads();
+        Natives.trySetMaxSizeVirtualMemory();
 
         // init lucene random seed. it will use /dev/urandom where available:
         StringHelper.randomId();

core/src/main/java/org/elasticsearch/bootstrap/Natives.java

@@ -99,6 +99,22 @@ final class Natives {
         JNANatives.trySeccomp(tmpFile);
     }
 
+    static void trySetMaxNumberOfThreads() {
+        if (!JNA_AVAILABLE) {
+            logger.warn("cannot getrlimit RLIMIT_NPROC because JNA is not available");
+            return;
+        }
+        JNANatives.trySetMaxNumberOfThreads();
+    }
+
+    static void trySetMaxSizeVirtualMemory() {
+        if (!JNA_AVAILABLE) {
+            logger.warn("cannot getrlimit RLIMIT_AS beacuse JNA is not available");
+            return;
+        }
+        JNANatives.trySetMaxSizeVirtualMemory();
+    }
+
     static boolean isSeccompInstalled() {
         if (!JNA_AVAILABLE) {
             return false;