[ruby/fiddle] Fix filenames for glibc SO files on alpha and ia64

(https://github.com/ruby/fiddle/pull/105)

Fixes [Bug #18645]

https://github.com/ruby/fiddle/commit/9a5a1dab1d

test/fiddle/helper.rb

@@ -49,8 +49,14 @@ when /linux/
     libm_so = libc_so
   else
     # glibc
-    libc_so = "libc.so.6"
-    libm_so = "libm.so.6"
+    case RUBY_PLATFORM
+    when /alpha-linux/, /ia64-linux/
+      libc_so = "libc.so.6.1"
+      libm_so = "libm.so.6.1"
+    else
+      libc_so = "libc.so.6"
+      libm_so = "libm.so.6"
+    end
   end
 when /mingw/, /mswin/
   require "rbconfig"