Fix path to racc in test/mri/tests/racc/helper.rb

* The tests pass but they are slow so exclude them.

Author: eregon

test/mri/failing.exclude

@@ -45,6 +45,7 @@ ruby/test_pattern_matching.rb
 # Too slow
 
 test_extlibs.rb
+racc/test_racc_command.rb
 
 # Other issues
 

test/mri/tests/racc/helper.rb

@@ -22,6 +22,7 @@ class TestCase < Test::Unit::TestCase
     TEST_DIR = test_dir
     racc = File.join(PROJECT_DIR, 'bin', 'racc')
     racc = File.join(PROJECT_DIR, '..', 'libexec', 'racc') unless File.exist?(racc)
+    racc = RbConfig::CONFIG["bindir"] + '/racc' if defined?(::TruffleRuby)
     RACC = racc
     ASSET_DIR = File.join(TEST_DIR, 'assets') # test grammars
     REGRESS_DIR  = File.join(TEST_DIR, 'regress') # known-good generated outputs