seccomp: install output atomically

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/output.go

@@ -0,0 +1,13 @@
+package internal
+
+import (
+	"git.gensokyo.uk/security/fortify/internal/fmsg"
+	"git.gensokyo.uk/security/fortify/seccomp"
+)
+
+func InstallFmsg(verbose bool) {
+	fmsg.Store(verbose)
+	if verbose {
+		seccomp.SetOutput(fmsg.Verbose)
+	}
+}