install.texi (Building a native compiler): Document new bootstrap-lto-noplugin configuration.

	* doc/install.texi (Building a native compiler): Document new
	bootstrap-lto-noplugin configuration.  Mention that bootstrap-lto
	configuration assumes that the host supports the linker plugin.

From-SVN: r221688

gcc/doc/install.texi

@@ -2525,7 +2525,10 @@ version 2.21 or later).
 
 @item @samp{bootstrap-lto-noplugin}
 This option is similar to @code{bootstrap-lto}, but is intended for
-hosts that do not support the linker plugin.
+hosts that do not support the linker plugin. Please note that static
+libraries are not compiled with link time optimizations without
+linker plugin.  Since GCC middle-end and back-end are in libbackend.a,
+it means that only part of the frontend is actually LTO optimized.
 
 @item @samp{bootstrap-debug}
 Verifies that the compiler generates the same executable code, whether