[build] properly install compiler-rt from Xcode toolchain

Similarly to what was done for #25547, copy the compiler-rt built-ins
for embedded platforms from the Xcode toolchain into the new generated
one, so to avoid link time errors.

Addresses SR-12001, rdar://57837918

Author: edymtt

utils/build-script-impl

@@ -1281,6 +1281,36 @@ function cmake_config_opt() {
     fi
 }
 
+function copy_embedded_compiler_rt_builtins_from_darwin_host_toolchain() {
+    local clang_dest_dir=$1
+
+    HOST_CXX_DIR=$(dirname "${HOST_CXX}")
+    HOST_LIB_CLANG_DIR="${HOST_CXX_DIR}/../lib/clang"
+    DEST_LIB_CLANG_DIR="${clang_dest_dir}/lib/clang"
+
+    if [[ -d "${HOST_LIB_CLANG_DIR}" ]] && [[ -d "${DEST_LIB_CLANG_DIR}" ]]; then
+        DEST_CXX_BUILTINS_VERSION=$(ls "${DEST_LIB_CLANG_DIR}" | awk '{print $0}')
+        DEST_BUILTINS_DIR="${clang_dest_dir}/lib/clang/$DEST_CXX_BUILTINS_VERSION/lib/darwin"
+
+        if [[ -d "${DEST_BUILTINS_DIR}" ]]; then
+            for HOST_CXX_BUILTINS_PATH in "${HOST_LIB_CLANG_DIR}"/*; do
+                HOST_CXX_BUILTINS_DIR="${HOST_CXX_BUILTINS_PATH}/lib/darwin"
+                echo "copying compiler-rt embedded builtins from ${HOST_CXX_BUILTINS_DIR} into the local clang build directory ${DEST_BUILTINS_DIR}."
+
+                for OS in ios watchos tvos; do
+                    LIB_NAME="libclang_rt.$OS.a"
+                    HOST_LIB_PATH="$HOST_CXX_BUILTINS_DIR/$LIB_NAME"
+                    if [[ -f "${HOST_LIB_PATH}" ]]; then
+                        call cp "${HOST_LIB_PATH}" "${DEST_BUILTINS_DIR}/${LIB_NAME}"
+                    elif [[ "${VERBOSE_BUILD}" ]]; then
+                        echo "no file exists at ${HOST_LIB_PATH}"
+                    fi
+                done
+            done
+        fi
+    fi
+}
+
 #
 # Configure and build each product
 #
@@ -2249,31 +2279,7 @@ for host in "${ALL_HOSTS[@]}"; do
         # builtins for iOS/tvOS/watchOS to ensure that Swift's
         # stdlib can use compiler-rt builtins when targetting iOS/tvOS/watchOS.
         if [[ "${product}" = "llvm" ]] && [[ "${BUILD_LLVM}" = "1" ]] && [[ "$(uname -s)" = "Darwin" ]]; then
-            HOST_CXX_DIR=$(dirname "${HOST_CXX}")
-            HOST_LIB_CLANG_DIR="${HOST_CXX_DIR}/../lib/clang"
-            DEST_LIB_CLANG_DIR="$(build_directory_bin ${host} llvm)/../lib/clang"
-
-            if [[ -d "${HOST_LIB_CLANG_DIR}" ]] && [[ -d "${DEST_LIB_CLANG_DIR}" ]]; then
-                DEST_CXX_BUILTINS_VERSION=$(ls "${DEST_LIB_CLANG_DIR}" | awk '{print $0}')
-                DEST_BUILTINS_DIR="$(build_directory_bin ${host} llvm)/../lib/clang/$DEST_CXX_BUILTINS_VERSION/lib/darwin"
-
-                if [[ -d "${DEST_BUILTINS_DIR}" ]]; then
-                    for HOST_CXX_BUILTINS_PATH in "${HOST_LIB_CLANG_DIR}"/*; do
-                        HOST_CXX_BUILTINS_DIR="${HOST_CXX_BUILTINS_PATH}/lib/darwin"
-                        echo "copying compiler-rt embedded builtins from ${HOST_CXX_BUILTINS_DIR} into the local clang build directory ${DEST_BUILTINS_DIR}."
-
-                        for OS in ios watchos tvos; do
-                            LIB_NAME="libclang_rt.$OS.a"
-                            HOST_LIB_PATH="$HOST_CXX_BUILTINS_DIR/$LIB_NAME"
-                            if [[ -f "${HOST_LIB_PATH}" ]]; then
-                                call cp "${HOST_LIB_PATH}" "${DEST_BUILTINS_DIR}/${LIB_NAME}"
-                            elif [[ "${VERBOSE_BUILD}" ]]; then
-                                echo "no file exists at ${HOST_LIB_PATH}"
-                            fi
-                        done
-                    done
-                fi
-            fi
+            copy_embedded_compiler_rt_builtins_from_darwin_host_toolchain "$(build_directory_bin ${host} llvm)/.."
         fi
     done
 done
@@ -2780,6 +2786,13 @@ for host in "${ALL_HOSTS[@]}"; do
         build_dir=$(build_directory ${host} ${product})
 
         call env DESTDIR="${host_install_destdir}" "${CMAKE_BUILD[@]}" "${build_dir}" -- ${INSTALL_TARGETS}
+        
+        # When we are installing LLVM copy over the compiler-rt
+        # builtins for iOS/tvOS/watchOS to ensure that we don't
+        # have compiler crashes when building apps for such platforms.
+        if [[ "${product}" = "llvm" ]] && [[ ! -z "${LLVM_INSTALL_COMPONENTS}" ]] && [[ "$(uname -s)" = "Darwin" ]]; then
+            copy_embedded_compiler_rt_builtins_from_darwin_host_toolchain "${host_install_destdir}${host_install_prefix}"
+        fi
     done
 done