test/rdoc/test_rdoc_generator_json_index.rb: pend in test_generate in ppc64le.

We observed that this test randomly fails in the ruby/ruby Travis ppc64le case.
This commit is to pend the test_generate if the assertion for the generated
file's modified time fails in a ppc64le environment.

Note that I didn't use the word "Travis CI" or Travis CI specific environment variables
such as `TRAVIS` and `TRAVIS_CPU_ARCH`[1] in the code. Because I wanted to prioritize the
rdoc's independence from the ruby/ruby.

[1] https://docs.travis-ci.com/user/environment-variables/#default-environment-variables

Author: junaruga

test/rdoc/test_rdoc_generator_json_index.rb

@@ -104,6 +104,18 @@ def test_generate
     orig_file = Pathname(File.join srcdir, 'generator/template/json_index/js/navigation.js')
     generated_file = Pathname(File.join @tmpdir, 'js/navigation.js')
 
+    # The following assertion for the generated file's modified time randomly
+    # fails in a ppc64le environment.
+    # https://github.com/ruby/rdoc/issues/1048
+    if orig_file.mtime.inspect != generated_file.mtime.inspect &&
+      RUBY_PLATFORM =~ /powerpc64le/
+      pend <<~EOC
+        Unstable test in ppc64le.
+        <#{orig_file.mtime.inspect}> expected but was
+        <#{generated_file.mtime.inspect}>.
+      EOC
+    end
+
     # This is dirty hack on JRuby
     assert_equal orig_file.mtime.inspect, generated_file.mtime.inspect,
       '.js files should be the same timestamp of original'