build: When LTO is not enabled, add -fno-lto option

If any single dependency happens to have LTO enabled, then LTO will turn
on automatically by default. Instead, only do an LTO build if the user
requested it.

This can greatly speed up compilation times for developer builds without
forcing recompilation of dependencies that are compiled for LTO.

Change-Id: I9e79a94bd4e3d701b4b189f94a09120d6a58f0bd
Signed-off-by: Ben Walker <ben@nvidia.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/24651


Reviewed-by: Jim Harris <jim.harris@samsung.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>
Community-CI: Mellanox Build Bot