Objective C and C mixed

I want to mix Objective C and C with xcode and report the following error, I dragged the project directly into the project.:

C project at https://github.com/1322453976/ss


:-1: Multiple commands produce '/Users/sk/Library/Developer/Xcode/DerivedData/testss-btbfjjrvzekmtjcsljrmgstxcbnq/Build/Products/Debug-iphoneos/testss.app/control':

1) Target 'testss' (project 'testss') has copy command from '/Users/sk/Desktop/test/testss/ss/debian/control' to '/Users/sk/Library/Developer/Xcode/DerivedData/testss-btbfjjrvzekmtjcsljrmgstxcbnq/Build/Products/Debug-iphoneos/testss.app/control'

2) Target 'testss' (project 'testss') has copy command from '/Users/sk/Desktop/test/testss/ss/debian/tests/control' to '/Users/sk/Library/Developer/Xcode/DerivedData/testss-btbfjjrvzekmtjcsljrmgstxcbnq/Build/Products/Debug-iphoneos/testss.app/control'


/Users/sk/Desktop/test/testss/ss/libcork/src/libcork/core/version.c:10:10: 'libcork/config.h' file not found

Objective C and C mixed
 
 
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