Cherrypick upstream r240600, r240601

  Relax assertion in x86_64 byval argument handling for 32-bit pointers

    Byval argument pair formation assumes that if a type is less than 8 bytes
    it must be an integer and not a pointer, which is not true for x32 and NaCl.

    Relax the assertion and add a test for a codegen case that triggered it.

(reviewed upstream)

Review URL:
2 files changed