Merge commit 189b7393d from llvm git (by John Baldwin):

[lld][RISCV] Use an e_flags of 0 if there are only binary input files.

  Summary:
  If none of the input files are ELF object files (for example, when
  generating an object file from a single binary input file via "-b
  binary"), use a fallback value for the ELF header flags instead of
  crashing with an assertion failure.

  Reviewers: MaskRay, ruiu, espindola

  Reviewed By: MaskRay, ruiu

  Subscribers: kevans, grimar, emaste, arichardson, asb, rbar,
  johnrusso, simoncook, sabuasal, niosHD, kito-cheng, shiva0217,
  zzheng, edward-jones, rogfer01, MartinMosbeck, brucehoult, the_o,
  rkruppe, PkmX, jocewei, psnobl, benna, Jim, lenary, s.egerton,
  pzheng, sameer.abuasal, apazos, luismarques, llvm-commits, jrtc27

  Tags: #llvm

  Differential Revision: https://reviews.llvm.org/D71101

This is a prerequisite for building and linking hard- and soft-float
riscv worlds with clang and lld.

Requested by:	jhb
MFC after:	1 week
X-MFC-With:	r353358

contrib/llvm-project/lld/ELF/Arch/RISCV.cpp

@@ -105,7 +105,10 @@ static uint32_t getEFlags(InputFile *f) {
 }
 
 uint32_t RISCV::calcEFlags() const {
-  assert(!objectFiles.empty());
+  // If there are only binary input files (from -b binary), use a
+  // value of 0 for the ELF header flags.
+  if (objectFiles.empty())
+    return 0;
 
   uint32_t target = getEFlags(objectFiles.front());