Support DESTDIR for install and add build-system test

Signed-off-by: Yi Wu <yi.wu2@arm.com>

library/CMakeLists.txt

@@ -362,7 +362,7 @@ foreach(target IN LISTS tf_psa_crypto_library_targets)
                     RENAME "libmbedcrypto.so.${MBEDTLS_VERSION}"
             )
             install(CODE "
-                set(_libdir \"\${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}\")
+                set(_libdir \"\$ENV{DESTDIR}${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}\")
 
                 execute_process(COMMAND \"\${CMAKE_COMMAND}\" -E create_symlink
                                 \"libmbedcrypto.so.${MBEDTLS_VERSION}\"

tests/scripts/components-build-system.sh

@@ -155,6 +155,32 @@ support_test_cmake_as_package_install () {
     support_test_cmake_out_of_source
 }
 
+component_test_cmake_install_with_destdir () {
+    # Remove existing generated files so that we use the ones CMake
+    # generates
+    $MAKE_COMMAND neat
+
+    msg "install: cmake with DESTDIR staging"
+    MBEDTLS_ROOT_DIR="$PWD"
+    mkdir "$OUT_OF_SOURCE_DIR"
+    cd "$OUT_OF_SOURCE_DIR"
+    cmake -DGEN_FILES=ON -DENABLE_PROGRAMS=OFF -DENABLE_TESTING=OFF -DUSE_SHARED_MBEDTLS_LIBRARY=ON -DCMAKE_INSTALL_PREFIX:PATH=/usr "$MBEDTLS_ROOT_DIR"
+    make
+
+    DESTDIR="$OUT_OF_SOURCE_DIR/stage" make install
+
+    install_libdir="$(sed -n 's/^CMAKE_INSTALL_LIBDIR:PATH=//p' CMakeCache.txt)"
+    test -n "$install_libdir"
+    test -L "$OUT_OF_SOURCE_DIR/stage/usr/${install_libdir}/libmbedcrypto.so"
+
+    cd "$MBEDTLS_ROOT_DIR"
+    rm -rf "$OUT_OF_SOURCE_DIR"
+}
+
+support_test_cmake_install_with_destdir () {
+    support_test_cmake_out_of_source
+}
+
 component_build_cmake_custom_config_file () {
     # Make a copy of config file to use for the in-tree test
     cp "$CONFIG_H" include/mbedtls_config_in_tree_copy.h