test/fiddle/helper: remove special case for x86_64-linux

RUBY_PLATFORM is "x86_64-linux" on a 32-bit (x86) Ruby built and
running on a 64-bit Linux kernel.  I also have a /lib64
directory nowadays because I just installed multi-arch support
in userspace.  So, fall back to loading based in the size of a
packed "unsigned long" type instead of special-casing.

Tested with both x86 and x86_64 userspace on 64-bit Linux kernel,
as well as x86 with a 32-bit Linux kernel.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57309 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/fiddle/helper.rb

@@ -10,9 +10,6 @@ case RUBY_PLATFORM
 when /cygwin/
   libc_so = "cygwin1.dll"
   libm_so = "cygwin1.dll"
-when /x86_64-linux/
-  libc_so = "/lib64/libc.so.6"
-  libm_so = "/lib64/libm.so.6"
 when /linux/
   libdir = '/lib'
   case [0].pack('L!').size