Improve the description of LLD_LINK_GPL3

Specify liblto_plugin.so and try to distinguish from the usual linking
that happens when linking to libstdc++ or libgcc_s.

Author: tuliom

lld/CMakeLists.txt

@@ -177,7 +177,7 @@ if (LLD_DEFAULT_LD_LLD_IS_MINGW)
   add_definitions("-DLLD_DEFAULT_LD_LLD_IS_MINGW=1")
 endif()
 
-option(LLD_LINK_GPL3 "Allow LLD to link to GPLv3-licensed files")
+option(LLD_LINK_GPL3 "Allow LLD to link to GPLv3-licensed plugins, e.g. liblto_plugin.so")
 option(LLD_ENABLE_GNU_LTO "Enable support for GNU LTO plugin")
 if(!LLD_LINK_GPL3)
   # Support for GNU LTO require linking to liblto_plugin.so from GCC which is