toolchain: add a program for compiling ipc interface definitions

ifc can be used to compile .if files into self-contained header-only C
libraries, which can be used to send/receive messages that conform
to the described interface.

toolchain/ifc/parse.h

@@ -0,0 +1,12 @@
+#ifndef IFC_PARSE_H_
+#define IFC_PARSE_H_
+
+struct ctx;
+struct lex;
+struct interface_definition;
+
+extern struct interface_definition *parse_interface_definition(
+	struct ctx *ctx,
+	struct lex *lex);
+
+#endif