may include command line options.

The cgo tool will always invoke the C compiler with the source file's
directory in the include path; i.e. -I${SRCDIR} is always implied. This
means that if a header file foo/bar.h exists both in the source
directory and also in the system include directory (or some other place
specified by a -I flag), then "#include <foo/bar.h>" will always find the
local version in preference to any other version.