Rework how bindings are generated

Cargo.toml

@@ -8,20 +8,29 @@ edition = "2018"
 repository = "https://github.com/rust-xed/xed-sys"
 readme = "README.md"
 keywords = ["xed", "intel", "x86", "x86_64"]
-categories = ["encoding", "external-ffi-bindings", "hardware-support", "parsing"]
+categories = ["encoding", "external-ffi-bindings", "hardware-support", "parsing", "no_std"]
 
 [badges]
 appveyor  = { repository = "rust-xed/xed-sys" }
 travis-ci = { repository = "rust-xed/xed-sys" }
 
+[features]
+# Enable the enc2 module of XED.
+#
+# Note that this will somewhat dramatically slow down compilation of xed-sys.
+# The enc2 module involves a large amount of generated code and the resulting
+# bindgen definitions contain 40+MB of rust code.
+enc2 = ["bindgen"]
+
+# Generate bindings with bindgen at build-time instead of using the
+# pregenerated bindings.
+#
+# This will be slower but is required for certain feature combinations.
+bindgen = ["dep:bindgen"]
+
 [dependencies]
 
 [build-dependencies]
-bindgen = "0.69"
+bindgen = { version = "0.69", optional = true, features = ["experimental"] }
+cc = "1.0"
 target-lexicon = "0.12"
-
-[workspace]
-members = [
-  ".",
-  "build-tools"
-]