Set profile for rust build, based on 'release' profile, see
https://doc.rust-lang.org/cargo/reference/profiles.html#release
and devel/cargo/cargo.port.mk. The default doesn't work for i386.

Index: .cargo/config
--- .cargo/config.orig
+++ .cargo/config
@@ -3,3 +3,14 @@ replace-with = "vendored-sources"
 
 [source.vendored-sources]
 directory = "vendor"
+
+[profile.release]
+opt-level = 2
+debug = 0
+debug-assertions = false
+overflow-checks = false
+lto = false
+panic = 'unwind'
+incremental = false
+codegen-units = 4
+rpath = false