Fix MSVC build (including on 2015), drop some workarounds for MSVC older than 2013.

The Windows client gyp files were missing proc_maps_linux.cc for the
unittest build. Adding that revealed some build errors due to it
unconditionally including <inttypes.h>. Removing the workarounds in
breakpad_types.h (and a few other places) made that build, which means
that Visual C++ 2013 is now our minimum supported version of MSVC.

Additionally I tried building with VC++ 2015 and fixed a few warnings
(which were failing the build because we have /WX enabled) to ensure
that that builds as well.

BUG=https://code.google.com/p/google-breakpad/issues/detail?id=669
R=mark@chromium.org

Review URL: https://codereview.chromium.org/1353893002 .

src/processor/dump_context.cc

@@ -38,9 +38,9 @@
 
 #ifdef _WIN32
 #include <io.h>
-#define PRIx64 "llx"
-#define PRIx32 "lx"
+#if defined(_MSC_VER) && _MSC_VER < 1900
 #define snprintf _snprintf
+#endif
 #else  // _WIN32
 #include <unistd.h>
 #endif  // _WIN32