Enable LTO

LTO was disabled 3 years ago because it was causing issues with certain
applications and games:
https://bugzilla.redhat.com/show_bug.cgi?id=1862771

Since then, support for LTO has improved upstream. Re-enable it.

mesa.spec

@@ -388,11 +388,6 @@ export MESON_PACKAGE_CACHE_DIR="%{cargo_registry}/"
 %rewrite_wrap_file unicode-ident
 %endif
 
-# We've gotten a report that enabling LTO for mesa breaks some games. See
-# https://bugzilla.redhat.com/show_bug.cgi?id=1862771 for details.
-# Disable LTO for now
-%define _lto_cflags %{nil}
-
 %meson \
   -Dplatforms=x11,wayland \
   -Ddri3=enabled \