Set the "asm" feature flag by default

Signed-off-by: Joe Richey <joerichey@google.com>

Cargo.toml

@@ -38,7 +38,7 @@ cc = { optional = true, version = "1.0" }
 panic-handler = { path = 'crates/panic-handler' }
 
 [features]
-default = ["compiler-builtins"]
+default = ["compiler-builtins", "asm"]
 
 # Some algorithms benefit from inline assembly, but some compiler backends do
 # not support it, so inline assembly is only enabled when this flag is set.