//	CGO_CFLAGS_DISALLOW
//		A regular expression specifying flags that must be disallowed
//		from appearing in #cgo CFLAGS source code directives.
//		Does not apply to the CGO_CFLAGS environment variable.
//	CGO_CPPFLAGS, CGO_CPPFLAGS_ALLOW, CGO_CPPFLAGS_DISALLOW
//		Like CGO_CFLAGS, CGO_CFLAGS_ALLOW, and CGO_CFLAGS_DISALLOW,
//		but for the C preprocessor.
//	CGO_CXXFLAGS, CGO_CXXFLAGS_ALLOW, CGO_CXXFLAGS_DISALLOW