Support building a cdylib and skip libbitcoinconsensus in wasm32

This, combined with
rust-bitcoin/rust-secp256k1#208 should get
us building in wasm again, hopefully without any future
complications due to WASM's lack of standard stdlibc.

Author: TheBlueMatt

lightning/Cargo.toml

@@ -10,6 +10,9 @@ Does most of the hard work, without implying a specific runtime, requiring clien
 Still missing tons of error-handling. See GitHub issues for suggested projects if you want to contribute. Don't have to bother telling you not to use this for anything serious, because you'd have to build a client around it to even try.
 """
 
+[lib]
+crate-type = ["cdylib", "rlib"]
+
 [features]
 # Supports tracking channels with a non-bitcoin chain hashes. Currently enables all kinds of fun DoS attacks.
 non_bitcoin_chain_hash_routing = []
@@ -26,7 +29,9 @@ bitcoin = "0.21"
 bitcoin_hashes = "0.7"
 secp256k1 = "0.15"
 
-[dev-dependencies.bitcoin]
+# Building libbitcoinconsensus in wasm32 requires a stdlibc, which is...complicated
+# Instead, just skip the script verification runs in wasm test runs.
+[target.'cfg(not(target_arch = "wasm32"))'.dev-dependencies.bitcoin]
 version = "0.21"
 features = ["bitcoinconsensus"]
 

lightning/src/ln/functional_test_utils.rs

@@ -467,6 +467,7 @@ pub fn create_announced_chan_between_nodes_with_value<'a, 'b, 'c, 'd>(nodes: &'a
 
 macro_rules! check_spends {
 	($tx: expr, $($spends_txn: expr),*) => {
+		#[cfg(not(target_arch = "wasm32"))]
 		{
 			$tx.verify(|out_point| {
 				$(