YJIT: Use ThinLTO for Rust parts in release mode

This reduces the code size of libyjit.a by a lot. On darwin it went from
23 MiB to 12 MiB for me. I chose ThinLTO over fat LTO for the relatively
fast build time; in case we need to debug release-build-only problems
it won't be painful.

Author: XrXr

common.mk

@@ -225,6 +225,7 @@ YJIT_RUSTC_ARGS = --crate-name=yjit \
 	--crate-type=staticlib \
 	--edition=2021 \
 	-g \
+	-C lto=thin \
 	-C opt-level=3 \
 	-C overflow-checks=on \
 	'--out-dir=$(CARGO_TARGET_DIR)/release/' \

yjit/Cargo.toml

@@ -45,3 +45,5 @@ opt-level = 3
 overflow-checks = true
 # Generate debug info
 debug = true
+# Use ThinLTO. Much smaller output for a small amount of build time increase.
+lto = "thin"