You could just explicitly declare where the header file is, like:
#include "/some/dir/file.h"
Or, like you were saying make a symlink to that file in a directory where your install of gcc already knows to look for the header files.
Make a symlink like this:
$ ln -s /root/include/originalFile /usr/include/linkFile
will create a link in /usr/include which references the file in /root/include/
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