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.
To allow additional flags, set CGO_CFLAGS_ALLOW to a regular expression
matching the new flags. To disallow flags that would otherwise be allowed,

// Go package ecosystem, in which code can be imported from any server,
// but it is also a potential security problem, if a malicious server finds a
// way to cause the invoked version control command to run unintended code.
//
// To balance the functionality and security concerns, the 'go get' command
// by default will only use git and hg to download code from public servers.