Enabling LTO yields substantial performance gains on both authoritative
and resolver benchmarks.
But since LTO defers many optimization passes to link time, enabling LTO
across the board would cause an increase in compilation time, as passes
that would be run only once would need to be run for each executable.
As a compromise, this commit adds a named-lto build option, that
compiles the individual object files with the -ffat-lto-object option
and then enables LTO only for the named executable. Object files are
reused between lib*.so and the named executable.
Meson is a modern build system that has seen a rise in adoption and some
version of it is available in almost every platform supported.
Compared to automake, meson has the following advantages:
* Meson provides a significant boost to the build and configuration time
by better exploiting parallelism.
* Meson is subjectively considered to be better in readability.
These merits alone justify experimenting with meson as a way of
improving development time and ergonomics. However, there are some
compromises to ensure the transition goes relatively smooth:
* The system tests currently rely on various files within the source
directory. Changing this requirement is a non-trivial task that can't
be currently justified. Currently the last compiled build directory
writes into the source tree which is in turn used by pytest.
* The minimum version supported has been fixed at 0.61. Increasing this
value will require choosing a baseline of distributions that can
package with meson. On the contrary, there will likely be an attempt
to decrease this value to ensure almost universal support for building
BIND 9 with meson.
