[ELF] - Versionscript: support wildcards for extern "c++" tag.

Previously for extern keyword only names in quotes (exact match) was supported.
Patch adds support for wildcards, so next scripts can be handled properly:

LIBSAMPLE_1.0 {
   global:            
     extern "C++" {  
       foo*;   
   };                  
 };

Differential revision: https://reviews.llvm.org/D23794

llvm-svn: 280067