[Bug #21255] Win32: Do not export __declspec(selectany) symbols

```
x64-vcruntime140-ruby350.def : error LNK2001: unresolved external symbol Avx2WmemEnabledWeakValue
```

Author: nobu

win32/mkexports.rb

@@ -110,6 +110,7 @@ def each_export(objs)
         case filetype
         when /OBJECT/, /LIBRARY/
           l.chomp!
+          next if (/^ .*\(pick any\)$/ =~ l)...true
           next if /^[[:xdigit:]]+ 0+ UNDEF / =~ l
           next unless /External/ =~ l
           next if /(?:_local_stdio_printf_options|v(f|sn?)printf(_s)?_l)\Z/ =~ l