[llvm-readelf] Update outdated URL

Update http://www.uxsglobal.com/developers/gabi/latest/ch4.eheader.html
to http://www.sco.com/developers/gabi/latest/ch4.eheader.html

Author: wenzhoumei

llvm/include/llvm/BinaryFormat/ELF.h

@@ -129,7 +129,7 @@ enum { EV_NONE = 0, EV_CURRENT = 1 };
 
 // Machine architectures
 // See current registered ELF machine architectures at:
-//    http://www.uxsglobal.com/developers/gabi/latest/ch4.eheader.html
+//    http://www.sco.com/developers/gabi/latest/ch4.eheader.html
 enum {
   EM_NONE = 0,           // No machine
   EM_M32 = 1,            // AT&T WE 32100