Mark RubyLanguage.getCurrentLanguage() and getCurrentContext() as neverPartOfCompilation

* neverPartOfCompilation() is much safer to use now that it is checked
  statically when building a Native Image.

Author: eregon

src/main/java/org/truffleruby/RubyContext.java

@@ -533,7 +533,7 @@ public Hashing getHashing() {
 
     public RubyLanguage getLanguageSlow() {
         CompilerAsserts.neverPartOfCompilation(
-                "@CachedLanguage or a final field in the node should be used so the RubyLanguage instance is constant in PE code");
+                "Use getLanguage() or @CachedLanguage instead, so the RubyLanguage instance is constant in PE code");
         return language;
     }
 

src/main/java/org/truffleruby/RubyLanguage.java

@@ -14,6 +14,7 @@
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.concurrent.locks.ReentrantLock;
 
+import com.oracle.truffle.api.CompilerAsserts;
 import com.oracle.truffle.api.CompilerDirectives;
 import com.oracle.truffle.api.instrumentation.AllocationReporter;
 import com.oracle.truffle.api.object.Shape;
@@ -327,10 +328,12 @@ protected void disposeContext(RubyContext context) {
     }
 
     public static RubyContext getCurrentContext() {
+        CompilerAsserts.neverPartOfCompilation("Use getContext() or @CachedContext instead in PE code");
         return getCurrentContext(RubyLanguage.class);
     }
 
     public static RubyLanguage getCurrentLanguage() {
+        CompilerAsserts.neverPartOfCompilation("Use getLanguage() or @CachedLanguage instead in PE code");
         return getCurrentLanguage(RubyLanguage.class);
     }