Reduce size of solang binary by only including webassembly backend

Signed-off-by: Sean Young <sean@mess.org>

Cargo.toml

@@ -13,7 +13,6 @@ lalrpop = "0.17.0"
 [dependencies]
 lalrpop-util = "0.17.0"
 regex = "0.2.1"
-inkwell = { git = "https://github.com/seanyoung/inkwell", branch = "llvm8-0" }
 num-bigint = "0.2"
 num-traits = "0.2.6"
 parity-wasm = "0.35"
@@ -27,3 +26,11 @@ serde_json = "1.0"
 serde = "1.0.90"
 ethabi = "7.0.0"
 ethereum-types = "0.5.2"
+
+[dependencies.inkwell]
+git = "https://github.com/TheDan64/inkwell"
+branch = "llvm8-0"
+features = ["target-webassembly", "llvm8-0"]
+
+[profile.release]
+lto = true