REGRESSION(276012@main): CMake fails with GObject-Introspection disabled

https://bugs.webkit.org/show_bug.cgi?id=269377

Reviewed by Michael Catanzaro and Philippe Normand.

* Source/WebKit/PlatformGTK.cmake: Quote the expansion of ${GI_VERSION}
  to ensure VERSION_GREATER_EQUAL has at least an empty string as value
  to compare against; otherwise when the variable is undefined there was
  no left-hand side of the comparison, which resulted in CMake erroring
  due to wrong syntax.

Canonical link: https://commits.webkit.org/276019@main

Source/WebKit/PlatformGTK.cmake

@@ -369,7 +369,7 @@ if (ENABLE_MEDIA_STREAM)
     )
 endif ()
 
-if (${GI_VERSION} VERSION_GREATER_EQUAL 1.79.2)
+if ("${GI_VERSION}" VERSION_GREATER_EQUAL 1.79.2)
     set(USE_GI_FINISH_FUNC_ANNOTATION 1)
 else ()
     set(USE_GI_FINISH_FUNC_ANNOTATION 0)