Cargo config improvements (#775)

* Move cargo config to correct location

* Add --no-rosegment to build params.
This helps with stack traces, and is necessary for some profilers.

backend/.cargo/config

@@ -1,3 +0,0 @@
-[build]
-rustflags = ["--cfg", "tokio_unstable", "-C", "link-arg=-fuse-ld=lld"]
-incremental = true

backend/.cargo/config.toml

@@ -0,0 +1,10 @@
+[build]
+rustflags = [
+    "--cfg",
+    "tokio_unstable",
+    "-C",
+    "link-arg=-fuse-ld=lld",
+    "-Clink-arg=-Wl,--no-rosegment",
+]
+incremental = true
+