add experimenal wasm32-wasi-threads support (#274)

* Add a variation of wasi-sdk.cmake for pthread-using apps

* Install wasi-sdk-pthread.cmake

* Build wasi-libc with THREAD_MODEL=posix as well

* wasi-sdk-pthread.cmake: target rename to wasm32-wasi-threads

after https://github.com/WebAssembly/wasi-libc/pull/381

Makefile

@@ -105,6 +105,12 @@ build/wasi-libc.BUILT: build/llvm.BUILT
 		AR=$(BUILD_PREFIX)/bin/llvm-ar \
 		NM=$(BUILD_PREFIX)/bin/llvm-nm \
 		SYSROOT=$(BUILD_PREFIX)/share/wasi-sysroot
+	$(MAKE) -C $(ROOT_DIR)/src/wasi-libc \
+		CC=$(BUILD_PREFIX)/bin/clang \
+		AR=$(BUILD_PREFIX)/bin/llvm-ar \
+		NM=$(BUILD_PREFIX)/bin/llvm-nm \
+		SYSROOT=$(BUILD_PREFIX)/share/wasi-sysroot \
+		THREAD_MODEL=posix
 	touch build/wasi-libc.BUILT
 
 build/compiler-rt.BUILT: build/llvm.BUILT build/wasi-libc.BUILT
@@ -196,6 +202,7 @@ build/config.BUILT:
 	cp src/config/config.sub src/config/config.guess $(BUILD_PREFIX)/share/misc
 	mkdir -p $(BUILD_PREFIX)/share/cmake
 	cp wasi-sdk.cmake $(BUILD_PREFIX)/share/cmake
+	cp wasi-sdk-pthread.cmake $(BUILD_PREFIX)/share/cmake
 	touch build/config.BUILT
 
 build: build/llvm.BUILT build/wasi-libc.BUILT build/compiler-rt.BUILT build/libcxx.BUILT build/config.BUILT

wasi-sdk-pthread.cmake

@@ -0,0 +1,31 @@
+# Cmake toolchain description file for the Makefile
+
+# This is arbitrary, AFAIK, for now.
+cmake_minimum_required(VERSION 3.4.0)
+
+set(CMAKE_SYSTEM_NAME WASI)
+set(CMAKE_SYSTEM_VERSION 1)
+set(CMAKE_SYSTEM_PROCESSOR wasm32)
+set(triple wasm32-wasi-threads)
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -pthread")
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pthread")
+
+if(WIN32)
+	set(WASI_HOST_EXE_SUFFIX ".exe")
+else()
+	set(WASI_HOST_EXE_SUFFIX "")
+endif()
+
+set(CMAKE_C_COMPILER ${WASI_SDK_PREFIX}/bin/clang${WASI_HOST_EXE_SUFFIX})
+set(CMAKE_CXX_COMPILER ${WASI_SDK_PREFIX}/bin/clang++${WASI_HOST_EXE_SUFFIX})
+set(CMAKE_AR ${WASI_SDK_PREFIX}/bin/llvm-ar${WASI_HOST_EXE_SUFFIX})
+set(CMAKE_RANLIB ${WASI_SDK_PREFIX}/bin/llvm-ranlib${WASI_HOST_EXE_SUFFIX})
+set(CMAKE_C_COMPILER_TARGET ${triple})
+set(CMAKE_CXX_COMPILER_TARGET ${triple})
+
+# Don't look in the sysroot for executables to run during the build
+set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
+# Only look in the sysroot (not in the host paths) for the rest
+set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)