Let exceptions bubble up while loading the core library

* It leads to much clearer errors rather than some NoMethodError
  from trying to print the backtrace early.
* Also avoids printing the backtrace multiple times.

Author: eregon

src/main/java/org/truffleruby/core/CoreLibrary.java

@@ -23,7 +23,6 @@
 import java.util.concurrent.ConcurrentMap;
 
 import com.oracle.truffle.api.RootCallTarget;
-import com.oracle.truffle.api.exception.AbstractTruffleException;
 import org.graalvm.shadowed.org.jcodings.transcode.EConvFlags;
 import org.truffleruby.RubyContext;
 import org.truffleruby.RubyLanguage;
@@ -776,10 +775,9 @@ public void loadRubyCoreLibraryAndPostBoot() {
             }
         } catch (IOException e) {
             throw CompilerDirectives.shouldNotReachHere(e);
-        } catch (AbstractTruffleException e) {
-            context.getDefaultBacktraceFormatter()
-                    .printRubyExceptionOnEnvStderr("Exception while loading core library:\n", e);
-            throw CompilerDirectives.shouldNotReachHere("couldn't load the core library", e);
+        } catch (Throwable e) {
+            System.err.println("\nException while loading core library:");
+            throw e;
         }
     }