Add some platform abstractions.

(This is a merge of http://go/wvgerrit/70303)

This adds a platform.h file to abstract some of the differences
between Windows and POSIX platforms.  This includes ntohl, setenv,
and ssize_t.

Bug: 122953649
Test: Android Unit Tests
Change-Id: I3235f3f284b53d24d7365ff3f4a06dcd9b403697

libwvdrmengine/cdm/core/src/buffer_reader.cpp

@@ -5,6 +5,7 @@
 #include "buffer_reader.h"
 
 #include "log.h"
+#include "platform.h"
 
 namespace wvcdm {
 

libwvdrmengine/cdm/core/src/crypto_session.cpp

@@ -7,7 +7,6 @@
 
 #include "crypto_session.h"
 
-#include <arpa/inet.h>  // needed for ntoh()
 #include <string.h>
 #include <algorithm>
 #include <iostream>
@@ -20,6 +19,7 @@
 #include "openssl/asn1.h"
 #include "openssl/sha.h"
 #include "openssl/x509v3.h"
+#include "platform.h"
 #include "properties.h"
 #include "pst_report.h"
 #include "string_conversions.h"

libwvdrmengine/cdm/core/src/initialization_data.cpp

@@ -4,7 +4,6 @@
 
 #include "initialization_data.h"
 
-#include <arpa/inet.h>
 #include <string.h>
 #include <sstream>
 
@@ -12,6 +11,7 @@
 #include "cdm_engine.h"
 #include "jsmn.h"
 #include "log.h"
+#include "platform.h"
 #include "properties.h"
 #include "string_conversions.h"
 #include "wv_cdm_constants.h"

libwvdrmengine/cdm/core/src/license.cpp

@@ -4,7 +4,6 @@
 
 #include "license.h"
 
-#include <arpa/inet.h>
 #include <sstream>
 #include <vector>
 
@@ -15,6 +14,7 @@
 #include "crypto_session.h"
 #include "device_files.h"
 #include "log.h"
+#include "platform.h"
 #include "policy_engine.h"
 #include "privacy_crypto.h"
 #include "properties.h"