Ignore unit test in TestBuiltin_strsplit

It is a special case of GNU-R.

(cherry picked from commit 7adec7d)

Author: Pavel Marek

com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/builtins/TestBuiltin_strsplit.java

@@ -177,6 +177,6 @@ public void testStrSplit() {
         // This test is ignored because it is a special case with an empty match at the beginning
         // and positive and negative lookarounds. Empty match at the beginning is normally
         // replaced by an empty character vector, but in this case gnur does not do that.
-        assertEval("strsplit('/some/path/to/somewhere' , '^(?=/)(?!//)|(?<!^)(?<!^/)/', perl = TRUE)");
+        assertEval(Ignored.ImplementationError, "strsplit('/some/path/to/somewhere' , '^(?=/)(?!//)|(?<!^)(?<!^/)/', perl = TRUE)");
     }
 }