PR#3410

(Imported from upstream's b7a4f98b15)

Change-Id: I382c12f205d9adbd418574f7938a1d55a07128e4

PNaCl needs OPENSSL_NO_ASM to work and a couple of cases were missing
because it hasn't previously been tested.

Additionally, it defined _BSD_SOURCE and others on the command line,
causing duplicate definition errors when defined in source code.

It's missing readdir_r.

It uses newlib, which appears to use u_short in socket.h without ever
defining it.

Change-Id: Ieccfc7365723d0521f6327eebe9f44a2afc57406
Reviewed-on: https://boringssl-review.googlesource.com/1140
Reviewed-by: Adam Langley <agl@google.com>

Initial fork from f2d678e6e8 (1.0.2 beta).

(This change contains substantial changes from the original and
effectively starts a new history.)