clang 5.+ (tested clang 7.0.0) seems to be attempting division-by-zero
and giving a very large number for static args to rb_funcall.

* include/ruby/ruby.h (rb_varargs_bad_length): relax check for clang
* ext/-test-/funcall/funcall.c: renamed from passing_block.c
  define extra_args_name function
* test/-ext-/funcall/test_funcall.rb: new test
  [ruby-core:85266] [Bug #14425]

From: Eric Wong <e@80x24.org>

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62116 b2dd03c8-39d4-4d8f-98ff-823fe69b080e