simplifying symbol table scopes

Linker cannot register extern import symbols initially because
the import object files are not available until all other object files are
resolved. To work around this, we create a stub weak symbol and assign
it to each import symbol. This allows linker to proceed. Once the import
object files are generated, linker replaces the stub symbol with
the actual ones from the import objects.

src/linker/lnk_symbol_table.c

@@ -21,15 +21,6 @@ lnk_make_lib_symbol(Arena *arena, String8 name, struct LNK_Lib *lib, U64 member_
   return symbol;
 }
 
-internal LNK_Symbol *
-lnk_make_import_symbol(Arena *arena, String8 name, String8 import_header)
-{
-  LNK_Symbol *symbol = push_array(arena, LNK_Symbol, 1);
-  symbol->name                = name;
-  symbol->u.imp.import_header = import_header;
-  return symbol;
-}
-
 internal LNK_Symbol *
 lnk_make_undefined_symbol(Arena *arena, String8 name, struct LNK_Obj *obj)
 {
@@ -299,9 +290,6 @@ lnk_can_replace_symbol(LNK_SymbolScope scope, LNK_Symbol *dst, LNK_Symbol *src)
       lnk_error(LNK_Error_InvalidPath, "unable to find a suitable replacement logic for symbol combination");
     }
   } break;
-  case LNK_SymbolScope_Import: {
-    lnk_error_multiply_defined_symbol(dst, src);
-  } break;
   case LNK_SymbolScope_Lib: {
     // link.exe picks symbol from lib that is discovered first
     can_replace = lnk_symbol_lib_is_before(src, dst);
@@ -344,10 +332,6 @@ lnk_on_symbol_replace(LNK_SymbolScope scope, LNK_Symbol *dst, LNK_Symbol *src)
     }
 #endif
   } break;
-  case LNK_SymbolScope_Import: {
-    // illegal to replace imports
-    InvalidPath;
-  } break;
   case LNK_SymbolScope_Lib: {
     // nothing to replace
   } break;