Keeping DEC Alpha support is difficult because there are no Alpha
machines available for toolchain developers, and even if there were,
no modern Linux distros still support Alpha. For example, Debian
dropped Alpha support in Debian 6.0. As a result, I cannot test my
linker with real-world programs.
In fact, I believe mold has never been able to link real-world large
programs. Object files for Alpha are compiled with the small code
model by default, so it is not easy to support it in the linker.
There's no means to verify that my implementation is correct for Alpha
because Alpha's psABI has never been published by DEC. The most
"reliable" source of correctness is GNU ld's source code and comments.
Last but not least, I believe there are literally zero mold/Alpha
users. Unlike some other retro computers like the m68k, Alpha doesn't
seem to get much love from the community, perhaps because the
availability of Alpha machines was limited in the first place, even in
the 90s.
Therefore, I'll remove Alpha support now. If there's someone who wants
to keep it, we can resurrect and re-test it.
This change should make the mold binary size a little smaller.
libtool mistakes mold 2.4.1 as GNU ld 2.4 and wrongly concludes that our
linker does not support anonymous versioning and suppresses some uses of
version scripts. That has been causing subtle compatibility issues with
programs that use libtool to create their .so files.
Here is the code that mistakes our linker as GNU ld:
https://git.savannah.gnu.org/cgit/libtool.git/tree/m4/libtool.m4?h=v2.4.7#n5066
As a workaround, I decided to bump our linker version so that the version
number is sufficiently large. This is admittedly ugly but I think it's the
simplest solution for the problem.
`CMakeLists.txt` declares a minimum CMake dependency on 3.14.
```
cmake_minimum_required(VERSION 3.13)
```
But the `--install` switch is only available since CMake 3.15, see
<https://stackoverflow.com/a/56457739>.
This commit updates the installation instructions in `README.md` so that
they work with CMake 3.14.
