[ELF] Omit PT_NOTE for SHT_NOTE without SHF_ALLOC

A non-alloc note section should not have a PT_NOTE program header.

Found while linking ghc (Haskell compiler) with lld on FreeBSD.
ghc emits a .debug-ghc-link-info note section (as the name suggests, it
contains link information) as a SHT_NOTE section without SHF_ALLOC set.

For this case ld.bfd does not emit a PT_NOTE segment for the
.debug-ghc-link-info section.  lld previously emitted a PT_NOTE with
p_vaddr = 0 and FreeBSD's rtld segfaulted when trying to parse a note at
address 0.

llvm.org/pr37361

Differential Revision:	https://reviews.llvm.org/D46623

llvm-svn: 331973