Fix cgo directives for multiple constraints

Author: anacrolix

go/cpossum/c-possum.go

@@ -4,8 +4,10 @@ package possumC
 // I think we trigger static linking on Linux because we don't want to have to specify the path to
 // the library at runtime. I can't seem to get CGO on macOS to do the same. I can't get a reliable
 // Windows system to get to the point I can actually build this, so I don't know how it works there.
-#cgo !windows && !darwin LDFLAGS: -L${SRCDIR}/../../target/debug -l:libpossum.a -lm
-#cgo darwin || windows LDFLAGS: -L${SRCDIR}/../../target/debug -lpossum
+// Also cgo directives seem to use the old build constraint syntax. Why the fuck isn't this stuff
+// documented?
+#cgo !windows,!darwin LDFLAGS: -L${SRCDIR}/../../target/debug -l:libpossum.a -lm
+#cgo darwin windows LDFLAGS: -L${SRCDIR}/../../target/debug -lpossum
 #include "possum.h"
 */
 import "C"