mkexports.rb: Revert removed flip-flop

This reverts commit 63ae1e3cb5d302e5229143c00152328166d26780.

win32/mkexports.rb

@@ -106,11 +106,7 @@ class Exports::Mswin < Exports
     objs = objs.collect {|s| s.tr('/', '\\')}
     filetype = nil
     objdump(objs) do |l|
-      if filetype
-        if /^\f/ =~ l
-          filetype = nil
-          next
-        end
+      if (filetype = l[/^File Type: (.+)/, 1])..(/^\f/ =~ l)
         case filetype
         when /OBJECT/, /LIBRARY/
           l.chomp!
@@ -132,8 +128,6 @@ class Exports::Mswin < Exports
           next
         end
         yield l.strip, is_data
-      else
-        filetype = l[/^File Type: (.+)/, 1]
       end
     end
     yield "strcasecmp", "msvcrt.stricmp"