cmake: Use GnuInstallDirs to customize install directories

Replace custom LIB_INSTALL_DIR with standard CMAKE_INSTALL_LIBDIR variable.
For backward compatibility, set CMAKE_INSTALL_LIBDIR if LIB_INSTALL_DIR is set.

Signed-off-by: Biswapriyo Nath <nathbappai@gmail.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7c6bbb7..8444917 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -39,6 +39,8 @@
     project("Mbed TLS" C)
 endif()
 
+include(GNUInstallDirs)
+
 # Set the project root directory.
 set(MBEDTLS_DIR ${CMAKE_CURRENT_SOURCE_DIR})
 
@@ -259,8 +261,7 @@
 endif(CMAKE_BUILD_TYPE STREQUAL "Coverage")
 
 if(LIB_INSTALL_DIR)
-else()
-    set(LIB_INSTALL_DIR lib)
+    set(CMAKE_INSTALL_LIBDIR "${LIB_INSTALL_DIR}")
 endif()
 
 if(ENABLE_ZLIB_SUPPORT)
diff --git a/ChangeLog.d/cmake_use_GnuInstallDirs.txt b/ChangeLog.d/cmake_use_GnuInstallDirs.txt
new file mode 100644
index 0000000..d848755
--- /dev/null
+++ b/ChangeLog.d/cmake_use_GnuInstallDirs.txt
@@ -0,0 +1,5 @@
+Changes
+   * cmake: Use GnuInstallDirs to customize install directories
+     Replace custom LIB_INSTALL_DIR variable with standard CMAKE_INSTALL_LIBDIR
+     variable. For backward compatibility, set CMAKE_INSTALL_LIBDIR if
+     LIB_INSTALL_DIR is set.
diff --git a/library/CMakeLists.txt b/library/CMakeLists.txt
index 1b2980d..798f42f 100644
--- a/library/CMakeLists.txt
+++ b/library/CMakeLists.txt
@@ -239,7 +239,7 @@
             PUBLIC MBEDTLS_USER_CONFIG_FILE="${MBEDTLS_USER_CONFIG_FILE}")
     endif()
     install(TARGETS ${target}
-            DESTINATION ${LIB_INSTALL_DIR}
+            DESTINATION ${CMAKE_INSTALL_LIBDIR}
             PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ)
 endforeach(target)