Fix an issue when compiling for web (#2820)

It would try to use the glfw on the system but we're cross-compiling for web where the implementation is provided by emscripten's team

src/CMakeLists.txt

@@ -38,7 +38,9 @@ set(raylib_sources
     )
 
 # <root>/cmake/GlfwImport.cmake handles the details around the inclusion of glfw
-include(GlfwImport)
+if (NOT ${PLATFORM} MATCHES "Web")
+    include(GlfwImport)
+endif ()
 
 # Sets additional platform options and link libraries for each platform
 # also selects the proper graphics API and version for that platform
@@ -68,6 +70,10 @@ else()
     endif ()
 endif()
 
+if (${PLATFORM} MATCHES "Web")
+    target_link_options(raylib PRIVATE "-sUSE_GLFW=3")
+endif()
+
 set_target_properties(raylib PROPERTIES
                       PUBLIC_HEADER "${raylib_public_headers}"
                       VERSION ${PROJECT_VERSION}