Use isNull message and NULL C constant in {call_}mmap

Author: steve-s

graalpython/com.oracle.graal.python.cext/posix/posix.c

@@ -508,7 +508,7 @@ int32_t call_system(const char *pathname) {
 
 void *call_mmap(int64_t length, int32_t prot, int32_t flags, int32_t fd, int64_t offset) {
     void *result = mmap(NULL, length, prot, flags, fd, offset);
-    return result == MAP_FAILED ? 0 : result;
+    return result == MAP_FAILED ? NULL : result;
 }
 
 int32_t call_munmap(void* address, int64_t length) {

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/runtime/NFIPosixSupport.java

@@ -1152,14 +1152,8 @@ public MMapHandle(Object pointer, long length) {
     public Object mmap(long length, int prot, int flags, int fd, long offset,
                     @Shared("invoke") @Cached InvokeNativeFunction invokeNode) throws PosixException {
         Object address = invokeNode.call(this, PosixNativeFunction.call_mmap, length, prot, flags, fd, offset);
-        try {
-            InteropLibrary interop = invokeNode.getResultInterop();
-            if (interop.fitsInInt(address) &&
-                            interop.asInt(address) == 0) {
-                throw newPosixException(invokeNode, getErrno(invokeNode));
-            }
-        } catch (UnsupportedMessageException e) {
-            throw CompilerDirectives.shouldNotReachHere(e);
+        if (invokeNode.getResultInterop().isNull(address)) {
+            throw newPosixException(invokeNode, getErrno(invokeNode));
         }
         return new MMapHandle(address, length);
     }