Pull in r353299 from upstream lld trunk (by George Rimar):

Pull in r353299 from upstream lld trunk (by George Rimar):

  Recommit r353293 "[LLD][ELF] - Set DF_STATIC_TLS flag for i386 target."

  With the following changes:
  1) Compilation fix:
  std::atomic<bool> HasStaticTlsModel = false; ->
  std::atomic<bool> HasStaticTlsModel{false};

  2) Adjusted the comment in code.

  Initial commit message:

  DF_STATIC_TLS flag indicates that the shared object or executable
  contains code using a static thread-local storage scheme.

  Patch checks if IE/LE relocations were used to check if the code uses
  a static model. If so it sets the DF_STATIC_TLS flag.

  Differential revision: https://reviews.llvm.org/D57749

Pull in r353378 from upstream lld trunk (by George Rimar):

  [LLD][ELF] - Set DF_STATIC_TLS flag for X64 target

  This is the same as D57749, but for x64 target.

  "ELF Handling For Thread-Local Storage" p41 says
  (https://www.akkadia.org/drepper/tls.pdf):
  R_X86_64_GOTTPOFF relocation is used for IE TLS models.
  Hence if linker sees this relocation we should add DF_STATIC_TLS flag.

  Differential revision: https://reviews.llvm.org/D57821

This adds support to lld for the DF_STATIC_TLS flag in shared objects,
which signals to the dynamic linker that the shared object requires
static thread local storage.

See also:	https://reviews.freebsd.org/D19072
MFC after:	1 week