The maximum nesting depth of #include files is 35.
For include files that are enclosed in double quotes
and do not begin with a /, the preprocessor will first search the current
directory, then the directory named in the -I option, and finally, in the standard include directory /usr/include.
For include files that are enclosed in < and > signs, the search path begins with the directory
named in the -I option and is completed in the standard include
directory, /usr/include. The current directory is not searched.
