Parse and store the value of the -O option.

llvm-svn: 251136
diff --git a/lld/ELF/Config.h b/lld/ELF/Config.h
index 00de985..612ad8f 100644
--- a/lld/ELF/Config.h
+++ b/lld/ELF/Config.h
@@ -66,6 +66,7 @@
   ELFKind EKind = ELFNoneKind;
   uint16_t EMachine = llvm::ELF::EM_NONE;
   uint64_t EntryAddr = -1;
+  unsigned Optimize = 0;
 };
 
 extern Configuration *Config;