[asan] Fix Android build for API >= 21.

/code/llvm/projects/compiler-rt/lib/sanitizer_common/sanitizer_linux.cc:971:8: error: address of function 'dl_iterate_phdr' will always evaluate to 'true' [-Werror,-Wpointer-bool-conversion]
  if (!dl_iterate_phdr)
      ~^~~~~~~~~~~~~~~
/code/llvm/projects/compiler-rt/lib/sanitizer_common/sanitizer_linux.cc:971:8: note: prefix with the address-of operator to silence this warning
  if (!dl_iterate_phdr)
       ^
       &

llvm-svn: 239321