Update CMakeLists.txt to install the cmake bindings in the right location (#737)

* Update CMakeLists.txt to install the cmake bindings in the right location

/usr/lib/cpprestsdk is not the correct FHS standard cmake location.
It should be placed in /usr/lib/<triplet>/cmake/cpprestsdk instead.

Same goes for libraries, support multiarch location if we use UNIX

* Revert changes to CPPREST_EXPORT_DIR. Use GNUInstallDirs on all platforms.

Author: LocutusOfBorg

Release/CMakeLists.txt

@@ -63,6 +63,7 @@ include(cmake/cpprest_find_zlib.cmake)
 include(cmake/cpprest_find_openssl.cmake)
 include(cmake/cpprest_find_websocketpp.cmake)
 include(CheckIncludeFiles)
+include(GNUInstallDirs)
 
 find_package(Threads REQUIRED)
 if(THREADS_HAVE_PTHREAD_ARG)

Release/src/CMakeLists.txt

@@ -253,9 +253,9 @@ if(CPPREST_INSTALL)
   install(
     TARGETS ${CPPREST_TARGETS}
     EXPORT cpprestsdk-targets
-    RUNTIME DESTINATION bin
-    LIBRARY DESTINATION lib
-    ARCHIVE DESTINATION lib
+    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
+    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
+    ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
   )
 
   configure_file(../cmake/cpprestsdk-config.in.cmake "${CMAKE_CURRENT_BINARY_DIR}/cpprestsdk-config.cmake" @ONLY)