Debug and release builds each compiled their own copy of every C
dependency and of the Rust staticlib, because build.zig threaded the
top-level optimize mode into all of them. Under dev_fast the deps also
picked up the bundled-CRT target query, so even the same mode could not
share objects with a plain build.
Dependencies now build in ReleaseFast for the requested target, the way
the prebuilt V8 archive already works. Debug and release builds share
one set of cached dependency objects, and debug binaries run TLS, HTML
parsing, regex and sqlite optimized. -Ddebug_deps restores the old
behaviour for stepping into a dependency.
The Rust staticlib can only be shared by dropping the Debug-only memstats
feature: its single export, html5ever_get_memory_usage, was declared on
the Zig side but never called, and it pulled a jemalloc build into every
cold debug build. The Makefile override that existed for jemalloc's
nested make goes with it.
Adrià Arrufat