ypkgcontext: Build with ffat-lto-objects when using LTO

In the rare case we have to ship any static files, ensure we build
with fat LTO objects so we ship actually usable static files as
LTO bytecode is non-portable. Any LTO bytecode will be manually
stripped from archive files.

ypkg2/ypkgcontext.py

@@ -41,10 +41,10 @@
 SIZE_FLAGS_CLANG = "-O2"
 
 # Allow optimizing for LTO
-LTO_FLAGS = "-flto=auto"
+LTO_FLAGS = "-flto=auto -ffat-lto-objects"
 
 # Allow optimizing for thin-lto
-THIN_LTO_FLAGS = "-flto=thin"
+THIN_LTO_FLAGS = "-flto=thin -ffat-lto-objects"
 
 # Allow optimizing for ICF all (identical code folding)
 ICF_ALL_FLAGS = "-Wl,--icf=all"