platform.in: Enable LTO by default

To opt out:

  %define optflags_lto %nil

To compile libs add `-ffat-lto-objects' like this:

  %define optflags_lto %optflags_lto -ffat-lto-objects

Do not use `-ffat-lto-objects' for anything except exported libs as it
doubles compile time.

platform.in

@@ -607,4 +607,7 @@ PATH=/usr/libexec/rpm-build:$PATH\
 # flags for compiling kernel
 %optflags_kernel	%nil
 
-%optflags_default	%optflags_core %optflags_warnings %optflags_debug %{!?_enable_debug:%{optflags_optimization}}
+# link time optimization
+%optflags_lto		-flto
+
+%optflags_default	%optflags_core %optflags_warnings %optflags_debug %{!?_enable_debug:%{optflags_optimization}} %optflags_lto