Auto-sync with upstream branch release/2.26/master
    
    Upstream commit: d300041c533a3d837c9f37a099bcc95466860e98
    
    - CVE-2018-6485, CVE-2018-6551: Fix integer overflows in internal
      memalign and malloc (#1542102, #1542119)
    - powerpc: Fix syscalls during early process initialization (swbz#22685)
    - math: Provide a C++ version of iseqsig (swbz#22377)
    - aarch: Rewrite elf_machine_load_address using _DYNAMIC symbol
    - x86-64: Properly align La_x86_64_retval to VEC_SIZE (swbz#22715)