Only apply max. optimizations in CI builds.

The average german man has a life expectancy of 78.7 years, or 689884.2 hours.
Assuming that Timo is 20 years old, he has rougly 514564.2 hours left on planet earth.
Also assuming that cross release builds took him 25 minutes before,
but 2-2.5x of that with the current release compilation config he wasted roughly an hour waiting for it to complete.
If he continued to work on Conduit for 20 more years (or 175320 hours),
and makes a release compilation about once per day, this means 7305 hours or 304 days wasted waiting for the rust compiler.
By cutting that back down to the original settings, he get's 182 days of his life back.
That's about 0.63% of his remaining life.
182 joyful days he can spend with family and loved ones.

.gitlab-ci.yml

@@ -27,6 +27,9 @@ variables:
       - cargohome
       - target/
     key: "build_cache-$TARGET-release"
+  variables:
+    CARGO_PROFILE_RELEASE_LTO=true
+    CARGO_PROFILE_RELEASE_CODEGEN_UNITS=1
   before_script:
     - 'echo "Building for target $TARGET"'
     - 'mkdir -p cargohome && CARGOHOME="cargohome"'

Cargo.toml

@@ -124,16 +124,15 @@ lto = 'thin'
 incremental = true
 
 [profile.release]
-lto = true
+lto = 'thin'
 incremental = true
-codegen-units = 1
+
+codegen-units=32
 # If you want to make flamegraphs, enable debug info:
 # debug = true
 
 # For releases also try to max optimizations for dependencies:
 [profile.release.build-override]
 opt-level = 3
-codegen-units = 1
 [profile.release.package."*"]
 opt-level = 3
-codegen-units = 1