// #include <png.h>
	import "C"

Alternatively, CPPFLAGS and LDFLAGS may be obtained via the pkg-config tool
using a '#cgo pkg-config:' directive followed by the package names.
For example:

	// #cgo pkg-config: png cairo
	// #include <png.h>
	import "C"

The default pkg-config tool may be changed by setting the PKG_CONFIG environment variable.

For security reasons, only a limited set of flags are allowed, notably -D, -U, -I, and -l.