jit backports to GCC 14

[David Malcolm]

I've backported the following patches from trunk to releases/gcc-14

testsuite, jit: fix test-error-pr63969-missing-driver.c
https://gcc.gnu.org/pipermail/gcc-patches/2024-October/665552.html
  Trunk: r15-4360-gf8dcb559e615db.
  GCC 14: r14-10854-g771873f0a95162

jit: reset state in varasm.cc [PR117275]
https://gcc.gnu.org/pipermail/gcc-patches/2024-October/666263.html
  Trunk: r15-4580-g779c0390e3b57d.
  GCC 14: r14-10855-g70f911bf547326

jit: fix leak of pending_assemble_externals_set [PR117275]
https://gcc.gnu.org/pipermail/gcc-patches/2024-October/666732.html
  Trunk: r15-4739-g7f41203f08b994.
  GCC 14: r14-10856-gacc0b9ff9cf1bc

Dave