[clang] [flang] [flang][Driver] Enables lto-partitions and fat-lto-object. (PR #158125)

[Leandro Lupori via cfe-commits]

luporl wrote:

This change also broke https://lab.llvm.org/buildbot/#/builders/130/builds/15415.
This bot uses gcc/ld instead of clang/lld.
It seems to me `flang/test/Driver/lto-lld-flags.f90` should only be run if lld is enabled.

https://github.com/llvm/llvm-project/pull/158125