Fix darwin platform.

Author: oraluben

substratevm/src/com.oracle.svm.truffle.nfi.posix/src/com/oracle/svm/truffle/nfi/posix/PosixTruffleNFIFeature.java

@@ -95,6 +95,7 @@ protected CCharPointer strdupImpl(CCharPointer src) {
         return PosixLibC.strdup(src);
     }
 
+    @Platforms(Platform.LINUX.class)
     private static PointerBase dlmopen(Lmid_t lmid, String filename, int mode) {
         try (CTypeConversion.CCharPointerHolder pathPin = CTypeConversion.toCString(filename)) {
             CCharPointer pathPtr = pathPin.get();
@@ -105,6 +106,7 @@ private static PointerBase dlmopen(Lmid_t lmid, String filename, int mode) {
     /**
      * A single linking namespace is created lazily and registered on the NFI context instance.
      */
+    @Platforms(Platform.LINUX.class)
     private static PointerBase loadLibraryInNamespace(long nativeContext, String name, int mode) {
         assert (mode & isolatedNamespaceFlag) == 0;
         Target_com_oracle_truffle_nfi_backend_libffi_LibFFIContextLinux context = SubstrateUtil.cast(getContext(nativeContext), Target_com_oracle_truffle_nfi_backend_libffi_LibFFIContextLinux.class);