Let sodium_malloc() and friends work on systems without protected memory.

On these systems, they become simple aliases for malloc() and friends.

Canaries could be added, but adding too much bloat for these rare systems
is probably not worth it, and malloc debuggers are better tools to use.
Merge branch 'master' of github.com:jedisct1/libsodium

* 'master' of github.com:jedisct1/libsodium:
  Let crypto_sign_open() accept NULL for the message length pointer Ditto for edwards25519sha512batch for consistency Add a _p suffix to lengths that are actually pointers for clarity
  remove extra pie check
  a second stab at detecting valid linker flags
  check to see if '-Wl,-pie' is supported before using it
  change '-pie' to '-Wl,-pie' to squash clang errors
  Use relative paths in sodium.h This make it easier to use sodium when bundled with another project.
  Make IPHONEOS_VERSION_MIN overridable
  Retry if open(2) is interrupted; set the CLOEXEC flag as well. Also retry if read(2) returns EAGAIN. This shouldn't happen in blocking mode, but it can't hurt either.
  Add libsodium-uninstalled.pc.in