Update BLST, add force-adx support (#1595)

## Issue Addressed

Closes #1504
Closes https://github.com/sigp/lighthouse/issues/1505

## Proposed Changes

* Update `blst` to the latest version, which is more portable and includes finer-grained compilation controls (see below).
* Detect the case where a binary has been explicitly compiled with ADX support but it's missing at runtime, and report a nicer error than `SIGILL`.

## Known Issues

* None. The previous issue with `make build-aarch64` (https://github.com/supranational/blst/issues/27), has been resolved.

## Additional Info

I think we should tweak our release process and our Docker builds so that we provide two options:

Binaries:

* `lighthouse`: compiled with `modern`/`force-adx`, for CPUs 2013 and newer
* `lighthouse-portable`: compiled with `portable` for older CPUs

Docker images:

* `sigp/lighthouse:latest`: multi-arch image with `modern` x86_64 and vanilla aarch64 binary
* `sigp/lighthouse:latest-portable`: multi-arch image with `portable` builds for x86_64 and aarch64

And relevant Docker images for the releases (as per https://github.com/sigp/lighthouse/pull/1574#issuecomment-687766141), tagged `v0.x.y` and `v0.x.y-portable`

lighthouse/Cargo.toml

@@ -9,6 +9,9 @@ edition = "2018"
 write_ssz_files = ["beacon_node/write_ssz_files"]
 # Compiles the BLS crypto code so that the binary is portable across machines.
 portable = ["bls/supranational-portable"]
+# Compiles BLST so that it always uses ADX instructions.
+# Compatible with processors from 2013 onwards.
+modern = ["bls/supranational-force-adx"]
 # Uses the slower Milagro BLS library, which is written in native Rust.
 milagro = ["bls/milagro"]
 

lighthouse/src/main.rs

@@ -16,6 +16,8 @@ pub const ETH2_CONFIG_FILENAME: &str = "eth2-spec.toml";
 fn bls_library_name() -> &'static str {
     if cfg!(feature = "portable") {
         "blst-portable"
+    } else if cfg!(feature = "modern") {
+        "blst-modern"
     } else if cfg!(feature = "milagro") {
         "milagro"
     } else {
@@ -181,6 +183,13 @@ fn run<E: EthSpec>(
         ));
     }
 
+    #[cfg(all(feature = "modern", target_arch = "x86_64"))]
+    if !std::is_x86_feature_detected!("adx") {
+        return Err(format!(
+            "CPU incompatible with optimized binary, please try Lighthouse portable build"
+        ));
+    }
+
     let debug_level = matches
         .value_of("debug-level")
         .ok_or_else(|| "Expected --debug-level flag".to_string())?;