// We need at least one runtime unit.
			if unit.Lib.Pkg == "runtime" {
				ctxt.runtimeCU = unit
			}

			cuabrv := dwarf.DW_ABRV_COMPUNIT
			if len(unit.Textp) == 0 {
				cuabrv = dwarf.DW_ABRV_COMPUNIT_TEXTLESS
			}
			unit.DWInfo = d.newdie(&dwroot, cuabrv, unit.Lib.Pkg)
			newattr(unit.DWInfo, dwarf.DW_AT_language, dwarf.DW_CLS_CONSTANT, int64(dwarf.DW_LANG_Go), 0)

	// #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.