try not to write absolute source file paths into C file position comments and...

try not to write absolute source file paths into C file position comments and use paths relative to build directory instead

Cython/Compiler/Scanning.py

@@ -210,6 +210,10 @@ class FileSourceDescriptor(SourceDescriptor):
         return lines
 
     def get_description(self):
+        try:
+            return os.path.relpath(self.path_description)
+        except ValueError:
+            # path not under current directory => use complete file path
             return self.path_description
 
     def get_error_description(self):