use compnerd/cmake's build of wasi-libc

[pchickey]

Using this PR to get the CI system to try building with wasi-libc's new CMamke based build system, by @compnerd

WebAssembly/wasi-libc#154 (comment)

[sunfishcode]

This is pre-existing, but we can remove the "llvm-" from these commands, as we install a plain "nm" and "ar" now.

[compnerd]

Drop the explicit install target and I think that it should work. I didn't really see an install target previously, so I did not create one. Currently, the CMake build will generate a complete sysroot under the sysroot directory in the build tree. (The last commit should also be unneeded)

[pchickey]

Subsequent build steps (compiler-rt) are calling the clang built prior to build, and requires some headers provided by wasi-libc. Clang's system include path is searching at $(PREFIX)/share/wasi-sysroot. So, we need to install wasi-libc to that location for the rest of the build to work, and for it to end up in the packages created by this repo.

[compnerd]

@pchickey sorry if what I was saying was unclear. What I meant is that something like this should work:

cmake -G Ninja \
 		-DCMAKE_SYSTEM_NAME=Generic \
 		-DCMAKE_AR=$(PREFIX)/bin/ar \
 		-DCMAKE_NM=$(PREFIX)/bin/nm \
 		-DCMAKE_C_COMPILER=$(PREFIX)/bin/clang \
 		-DCMAKE_C_COMPILER_WORKS=YES \
		-B build/wasi-libc \
 		-S $(ROOT_DIR)/src/wasi-libc
cmake --build build/wasi-libc

That will generate a proper sysroot in build/wasi-libc/sysroot. A cp -r build/wasi-libc/sysroot $(PREFIX)/share/wasi-sysroot should be sufficient to "install"

[pchickey]

@compnerd thanks, that fix got us through compiler-rt, but now libcxx is failing. Any ideas?

[compnerd]

-- Performing Test LIBCXX_SUPPORTS_STD_EQ_CXX14_FLAG
-- Performing Test LIBCXX_SUPPORTS_STD_EQ_CXX14_FLAG - Failed
-- Performing Test LIBCXX_SUPPORTS_STD_COLON_CXX14_FLAG
-- Performing Test LIBCXX_SUPPORTS_STD_COLON_CXX14_FLAG - Failed
  C++11 or greater is required but the compiler does not support c++14

Seems that -std=c++14 and /std:c++14 are both failing. Unfortunately, I cannot tell what is failing in the test :(. You could theoretically try -D LIBCXX_SUPPORTS_STD_EQ_CXX14_FLAG=YES as a workaround.

[pchickey]

I never got back to this and it isn't a priority, so closing for now. If anyone else wants to take this work on, feel free to re-open.