Use -unwindlib=libunwind instead of merging libunwind into libc++

This makes the build of libcxx a bit cleaner, and simplifies later
building and testing of libcxx.

build-compiler-rt.sh

@@ -100,7 +100,22 @@ for arch in $ARCHS; do
     $BUILDCMD ${CORES+-j$CORES}
     $BUILDCMD install
     mkdir -p "$PREFIX/$arch-w64-mingw32/bin"
-    if [ -n "$SANITIZERS" ]; then
+    if [ -z "$SANITIZERS" ]; then
+        # Building builtins only. If libunwind isn't built yet, linking of any
+        # executable will still fail as we're using -unwindlib=libunwind.
+        # Therefore, create a dummy libunwind.a (unless there's a real
+        # libunwind installed already) to let linking succeed.
+        #
+        # This is a workaround to avoid needing to specify -unwindlib=none
+        # for all linking until libunwind has been built. This avoids
+        # needing to build libunwind right away (allowing building plain C
+        # executables already now) and avoids needing to pass -unwindlib=none
+        # when configuring the libunwind build.
+        if [ ! -f $PREFIX/$arch-w64-mingw32/lib/libunwind.a ] && [ ! -f $PREFIX/$arch-w64-mingw32/lib/libunwind.dll.a ]; then
+            # Create an archive, don't add any members.
+            llvm-ar rcs $PREFIX/$arch-w64-mingw32/lib/libunwind.a
+        fi
+    else
         mv "$PREFIX/lib/clang/$CLANG_VERSION/lib/windows/"*.dll "$PREFIX/$arch-w64-mingw32/bin"
     fi
     cd ..

build-libcxx.sh

@@ -193,15 +193,6 @@ build_all() {
         cd build-$arch-$type
         $BUILDCMD ${CORES+-j$CORES}
         $BUILDCMD install
-        if [ "$type" = "shared" ]; then
-            llvm-ar qcsL \
-                "$PREFIX/$arch-w64-mingw32/lib/libc++.dll.a" \
-                "$PREFIX/$arch-w64-mingw32/lib/libunwind.dll.a"
-        else
-            llvm-ar qcsL \
-                "$PREFIX/$arch-w64-mingw32/lib/libc++.a" \
-                "$PREFIX/$arch-w64-mingw32/lib/libunwind.a"
-        fi
         cd ..
     done
     cd ..
@@ -211,3 +202,13 @@ build_all() {
 # work when linking against the DLL, but not vice versa.
 [ -z "$BUILD_SHARED" ] || build_all shared
 [ -z "$BUILD_STATIC" ] || build_all static
+
+# Remove dummy placeholder libunwind.a. If we've built a static version, it
+# already was overwritten with a proper one, but if only building a shared
+# version, remove the dummy one to avoid surprises.
+for arch in $ARCHS; do
+    # Only remove the file if it contains no members.
+    if [ -f $PREFIX/$arch-w64-mingw32/lib/libunwind.a ] && [ "$(llvm-ar t $PREFIX/$arch-w64-mingw32/lib/libunwind.a)" = "" ]; then
+        rm $PREFIX/$arch-w64-mingw32/lib/libunwind.a
+    fi
+done

build-llvm.sh

@@ -157,6 +157,7 @@ if [ -n "$HOST" ]; then
     # the frontend wrappers, but this makes sure they are enabled by
     # default if that wrapper is bypassed as well.
     CMAKEFLAGS="$CMAKEFLAGS -DCLANG_DEFAULT_RTLIB=compiler-rt"
+    CMAKEFLAGS="$CMAKEFLAGS -DCLANG_DEFAULT_UNWINDLIB=libunwind"
     CMAKEFLAGS="$CMAKEFLAGS -DCLANG_DEFAULT_CXX_STDLIB=libc++"
     CMAKEFLAGS="$CMAKEFLAGS -DCLANG_DEFAULT_LINKER=lld"
     BUILDDIR=$BUILDDIR-$HOST

wrappers/clang-target-wrapper.c

@@ -224,6 +224,7 @@ int _tmain(int argc, TCHAR* argv[]) {
     exec_argv[arg++] = _T("-target");
     exec_argv[arg++] = target;
     exec_argv[arg++] = _T("-rtlib=compiler-rt");
+    exec_argv[arg++] = _T("-unwindlib=libunwind");
     exec_argv[arg++] = _T("-stdlib=libc++");
     exec_argv[arg++] = _T("-fuse-ld=lld");
     exec_argv[arg++] = _T("-Qunused-arguments");

wrappers/clang-target-wrapper.sh

@@ -84,6 +84,7 @@ esac
 
 FLAGS="$FLAGS -target $TARGET"
 FLAGS="$FLAGS -rtlib=compiler-rt"
+FLAGS="$FLAGS -unwindlib=libunwind"
 FLAGS="$FLAGS -stdlib=libc++"
 FLAGS="$FLAGS -fuse-ld=lld"
 FLAGS="$FLAGS -Qunused-arguments"