Build libcxx and libcxxabi via llvm-project/runtimes

This is the new method to build runtimes as of LLVM 12, and the previous
standalone method is deprecated since LLVM 14 and unsupported since
LLVM 15 (llvm/llvm-project@6f17768)

Building libcxx and libcxxabi in one go simplifies the setup necessary
as:
- tests CMakeLists.txt have some wrong dependencies which would need
  to be worked around.
- LIBCXXABI_LIBCXX_INCLUDES is not recognized when building separately
  and passing -I paths via the command line yields msys path munging
  problems on Windows.

This effectively drops support for LLVM 11 and older.

Makefile

@@ -126,7 +126,7 @@ build/compiler-rt.BUILT: build/llvm.BUILT build/wasi-libc.BUILT
 	cp -R $(ROOT_DIR)/build/llvm/lib/clang $(BUILD_PREFIX)/lib/
 	touch build/compiler-rt.BUILT
 
-# Flags for libcxx.
+# Flags for libcxx and libcxxabi.
 LIBCXX_CMAKE_FLAGS = \
     -DCMAKE_C_COMPILER_WORKS=ON \
     -DCMAKE_CXX_COMPILER_WORKS=ON \
@@ -136,11 +136,13 @@ LIBCXX_CMAKE_FLAGS = \
     -DCMAKE_STAGING_PREFIX=$(PREFIX)/share/wasi-sysroot \
     -DLLVM_CONFIG_PATH=$(ROOT_DIR)/build/llvm/bin/llvm-config \
     -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON \
+    -DCXX_SUPPORTS_CXX11=ON \
     -DLIBCXX_ENABLE_THREADS:BOOL=OFF \
     -DLIBCXX_HAS_PTHREAD_API:BOOL=OFF \
     -DLIBCXX_HAS_EXTERNAL_THREAD_API:BOOL=OFF \
     -DLIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY:BOOL=OFF \
     -DLIBCXX_HAS_WIN32_THREAD_API:BOOL=OFF \
+    -DLLVM_COMPILER_CHECKED=ON \
     -DCMAKE_BUILD_TYPE=RelWithDebugInfo \
     -DLIBCXX_ENABLE_SHARED:BOOL=OFF \
     -DLIBCXX_ENABLE_EXPERIMENTAL_LIBRARY:BOOL=OFF \
@@ -150,30 +152,6 @@ LIBCXX_CMAKE_FLAGS = \
     -DLIBCXX_CXX_ABI_INCLUDE_PATHS=$(LLVM_PROJ_DIR)/libcxxabi/include \
     -DLIBCXX_HAS_MUSL_LIBC:BOOL=ON \
     -DLIBCXX_ABI_VERSION=2 \
-    -DWASI_SDK_PREFIX=$(BUILD_PREFIX) \
-    --debug-trycompile
-
-build/libcxx.BUILT: build/llvm.BUILT build/compiler-rt.BUILT build/wasi-libc.BUILT
-	# Do the build.
-	mkdir -p build/libcxx
-	cd build/libcxx && cmake -G Ninja $(LIBCXX_CMAKE_FLAGS) \
-		-DCMAKE_SYSROOT=$(BUILD_PREFIX)/share/wasi-sysroot \
-		-DCMAKE_C_FLAGS="$(DEBUG_PREFIX_MAP)" \
-		-DCMAKE_CXX_FLAGS="$(DEBUG_PREFIX_MAP)" \
-		-DLIBCXX_LIBDIR_SUFFIX=$(ESCAPE_SLASH)/wasm32-wasi \
-		$(LLVM_PROJ_DIR)/libcxx
-	ninja $(NINJA_FLAGS) -C build/libcxx
-	# Do the install.
-	DESTDIR=$(DESTDIR) ninja $(NINJA_FLAGS) -C build/libcxx install
-	touch build/libcxx.BUILT
-
-# Flags for libcxxabi.
-LIBCXXABI_CMAKE_FLAGS = \
-    -DCMAKE_C_COMPILER_WORKS=ON \
-    -DCMAKE_CXX_COMPILER_WORKS=ON \
-    -DCMAKE_AR=$(BUILD_PREFIX)/bin/ar \
-    -DCMAKE_MODULE_PATH=$(ROOT_DIR)/cmake \
-    -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON \
     -DLIBCXXABI_ENABLE_EXCEPTIONS:BOOL=OFF \
     -DLIBCXXABI_ENABLE_SHARED:BOOL=OFF \
     -DLIBCXXABI_SILENT_TERMINATE:BOOL=ON \
@@ -183,31 +161,25 @@ LIBCXXABI_CMAKE_FLAGS = \
     -DLIBCXXABI_BUILD_EXTERNAL_THREAD_LIBRARY:BOOL=OFF \
     -DLIBCXXABI_HAS_WIN32_THREAD_API:BOOL=OFF \
     -DLIBCXXABI_ENABLE_PIC:BOOL=OFF \
-    -DCXX_SUPPORTS_CXX11=ON \
-    -DLLVM_COMPILER_CHECKED=ON \
-    -DCMAKE_BUILD_TYPE=RelWithDebugInfo \
-    -DLIBCXXABI_LIBCXX_PATH=$(LLVM_PROJ_DIR)/libcxx \
-    -DLIBCXXABI_LIBCXX_INCLUDES=$(BUILD_PREFIX)/share/wasi-sysroot/include/c++/v1 \
-    -DLLVM_CONFIG_PATH=$(ROOT_DIR)/build/llvm/bin/llvm-config \
-    -DCMAKE_TOOLCHAIN_FILE=$(ROOT_DIR)/wasi-sdk.cmake \
-    -DCMAKE_STAGING_PREFIX=$(PREFIX)/share/wasi-sysroot \
     -DWASI_SDK_PREFIX=$(BUILD_PREFIX) \
     -DUNIX:BOOL=ON \
     --debug-trycompile
 
-build/libcxxabi.BUILT: build/libcxx.BUILT build/llvm.BUILT
+build/libcxx.BUILT: build/llvm.BUILT build/compiler-rt.BUILT build/wasi-libc.BUILT
 	# Do the build.
-	mkdir -p build/libcxxabi
-	cd build/libcxxabi && cmake -G Ninja $(LIBCXXABI_CMAKE_FLAGS) \
+	mkdir -p build/libcxx
+	cd build/libcxx && cmake -G Ninja $(LIBCXX_CMAKE_FLAGS) \
 		-DCMAKE_SYSROOT=$(BUILD_PREFIX)/share/wasi-sysroot \
 		-DCMAKE_C_FLAGS="$(DEBUG_PREFIX_MAP)" \
 		-DCMAKE_CXX_FLAGS="$(DEBUG_PREFIX_MAP)" \
+		-DLIBCXX_LIBDIR_SUFFIX=$(ESCAPE_SLASH)/wasm32-wasi \
 		-DLIBCXXABI_LIBDIR_SUFFIX=$(ESCAPE_SLASH)/wasm32-wasi \
-		$(LLVM_PROJ_DIR)/libcxxabi
-	ninja $(NINJA_FLAGS) -C build/libcxxabi
+		-DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \
+		$(LLVM_PROJ_DIR)/runtimes
+	ninja $(NINJA_FLAGS) -C build/libcxx
 	# Do the install.
-	DESTDIR=$(DESTDIR) ninja $(NINJA_FLAGS) -C build/libcxxabi install
-	touch build/libcxxabi.BUILT
+	DESTDIR=$(DESTDIR) ninja $(NINJA_FLAGS) -C build/libcxx install
+	touch build/libcxx.BUILT
 
 build/config.BUILT:
 	mkdir -p $(BUILD_PREFIX)/share/misc
@@ -216,7 +188,7 @@ build/config.BUILT:
 	cp wasi-sdk.cmake $(BUILD_PREFIX)/share/cmake
 	touch build/config.BUILT
 
-build: build/llvm.BUILT build/wasi-libc.BUILT build/compiler-rt.BUILT build/libcxxabi.BUILT build/libcxx.BUILT build/config.BUILT
+build: build/llvm.BUILT build/wasi-libc.BUILT build/compiler-rt.BUILT build/libcxx.BUILT build/config.BUILT
 
 strip: build/llvm.BUILT
 	./strip_symbols.sh $(BUILD_PREFIX)