When the cgo directives are parsed, any occurrence of the string ${SRCDIR}
will be replaced by the absolute path to the directory containing the source
file. This allows pre-compiled static libraries to be included in the package
directory and linked properly.
For example if package foo is in the directory /go/src/foo:

	// #cgo LDFLAGS: -L${SRCDIR}/libs -lfoo

Will be expanded to:

	// #cgo LDFLAGS: -L/go/src/foo/libs -lfoo