Win32: Add library name suffix to pkg-config file

Closes #2386

This was adapted to 3.3-stable from
93a3ba8080.

CMakeLists.txt

@@ -45,6 +45,7 @@ if (BUILD_SHARED_LIBS AND UNIX)
 else()
     set(GLFW_LIB_NAME glfw3)
 endif()
+set(GLFW_LIB_NAME_SUFFIX "")
 
 if (GLFW_VULKAN_STATIC)
     if (BUILD_SHARED_LIBS)
@@ -196,6 +197,10 @@ if (_GLFW_WIN32)
     if (GLFW_USE_HYBRID_HPG)
         set(_GLFW_USE_HYBRID_HPG 1)
     endif()
+
+    if (BUILD_SHARED_LIBS)
+        set (GLFW_LIB_NAME_SUFFIX "dll")
+    endif()
 endif()
 
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