feat(makefile) Simplify the prelude + build-capi includes all available compilers

[Hywan]

Description

This PR contains 2 parts. Don't be afraid, it's very small changes, and it's easy to follow.

How to Review

I recommend to review the PR patch by patch, it's way simpler than reading the final diff.
Note that the matrix (the table in the Makefile documentation) is updated patch after patch,
so this part should ideally be reviewed in the final diff.

The final Makefile is here, https://github.com/Hywan/wasmer/blob/feat-c-api-build-lib-with-all-compilers-and-engines/Makefile, and it's even easier to read now.

Part 1, The Matrix

The set of patches writes a matrix: platform x architecture x compiler x engine x libc, and for each combination, says if it's supported or not.

This set of patches updates the “prelude” of the Makefile to make it clearler and easier to read, regarding the matrix.

1. adb7c59, This patch removes the UNAME_S and ARCH variables. It replaces
   them with IS_WINDOWS, IS_LINUX, IS_DARWIN, IS_AMD64, and
   IS_AARCH64 variables. It makes the code easier to read and simpler
   to maintain.

   This patch also documents the large matrix of platform x architecture
   x compiler x engine x lib support.

2. 659bdb0, This patch removes a possible duplication of the llvm value inside
   the compilers variable if both LLVM 10 and 11 are available.

   This patch also checks for LLVM 11 before LLVM 10.

3. 7b38752, This patch moves all the assignments of compilers in the same place
   for the sake of clarity.

4. 006c653, This patch renames the test_compilers_engines variable to
   compilers_engines. We can use this variable for test purposes, but more
   importantly, it defines all the pair (compiler, engine), make it that clear.

   I've decided to separate this patch from the followings to facilitate the review.

5. 67a1dfe, This patch handles the (cranelift, *) pairs in a single place.

6. f3c729d, This patch handles the (llvm, *) pairs in a single place.

7. 1054e51, This patch handles the (singlepass, *) pairs in a single place.

8. 07e48b4 , This patch adds the HAS_<compiler> variables, it makes the code
   easier to read.

9. 06d543a, 660daba, 95dcb04, 6721769, and 62c7889 are small improvements.

10. 0a0b7f8, This patch introduces ENABLE_<compiler> variables, that can be
    overriden by the user to force to enable or to disable a compiler. They replace
    the HAS_<compiler> variables.

Part 2, libwasmer includes all available compilers

1. 387a753, This patch updates the build-capi rule to no longer uses Cranelift by default,
   but to include/enable all the available compilers.

2. f846a0d, This patch explains test-capi with a little bit more details.

   This patch also introduces the test-capi-all rule. Why? test-capi will continue to
   build and to test the C API with a single compiler enabled, so that it's the default one
   that will be used by the tests. But we also want to test the libwasmer we are giving
   to the users! That's what test-capi-all does. Notice that the test-capi rule depends
   test-capi-all, so we don't need to update the CI.

Closes #2063

Review

• Add a short description of the the change to the CHANGELOG.md file

[Hywan]

bors try

[bors]

try

Build failed:

• Code lint

[Hywan]

@MarkMcCaskey With ed34e48, LLVM is always removed from the C API when built with make build-capi or make test-capi.

[Hywan]

bors try

[bors]

try

Already running a review

[Hywan]

Run is here https://github.com/wasmerio/wasmer/runs/1912092129

[Hywan]

PR is green, modulo our sccache issue on Windows.

[nlewycky]

Update to pick up fix to sccache issue.

[nlewycky]

bors try

[bors]

try

Already running a review

[syrusakbary]

bors try

[bors]

try

Already running a review

[syrusakbary]

bors try-

[syrusakbary]

bors try

[syrusakbary]

Not reviewing any of the specifics, just want to say again that I don't think we can ship libwasmer with LLVM until we fix the linking issues regarding LLVM. Otherwise users will need zlib, curses, and potentially other libraries even when not building against LLVM. If this is an unfixable problem, which I don't think anyone is saying it is, compiler-llvm (or maybe every compiler) should be shipped in its own static library.

@jubianchi can you check if that still the case (zlib/curses requirement when embedding LLVM in the wasmer c api)?
I thought we fixed by using our custom llvm builds, but that might not be the case

[bors]

try

Build failed:

• Test cross-compile on linux

[Hywan]

bors try

[bors]

try

Build succeeded:

• Code lint
• Test on windows-x64
• Test on linux-x64
• Test on linux-aarch64
• Test on macos-x64
• Test cross-compile on linux
• Test cross-compile on macos
• Audit

[Hywan]

bors r+

[bors]

Build succeeded:

• Audit
• Code lint
• Test cross-compile on linux
• Test cross-compile on macos
• Test on linux-aarch64
• Test on linux-x64
• Test on macos-x64
• Test on windows-x64