Use external wordsize to get emulator build arch

Calling erlang:system_info(wordsize) yields the internal word size of
the Erlang emulator. But due to the halfword emulator, need to pass
{wordsize, external} instead to get the word size, or pointer size, as
seen by external code such as NIFs. The halfword emulator has 4 byte
internal words but 8 byte external words due to 64-bit compilation,
which means NIFs for the halfword emulator also have to be compiled
64-bit. But just passing wordsize is equivalent to passing {wordsize,
internal}, which does not indicate the pointer size for the halfword
emulator.

Older versions of Erlang do not support {wordsize, external}, though,
so continue to pass just wordsize for those versions.

src/rebar_erlc_compiler.erl

@@ -52,7 +52,8 @@
 %%
 %%                OtpRelease = erlang:system_info(otp_release).
 %%                SysArch = erlang:system_info(system_architecture).
-%%                Words = integer_to_list(8 * erlang:system_info(wordsize)).
+%%                Words = integer_to_list(8 *
+%%                            erlang:system_info({wordsize, external})).
 %%
 %%              E.g. to define HAVE_SENDFILE only on systems with
 %%              sendfile(), to define BACKLOG on Linux/FreeBSD as 128,

src/rebar_port_compiler.erl

@@ -398,7 +398,14 @@ default_env() ->
      {"DRV_LDFLAGS", "-shared $ERL_LDFLAGS"},
      {"darwin", "DRV_LDFLAGS",
       "-bundle -flat_namespace -undefined suppress $ERL_LDFLAGS"},
-     {"ERLANG_ARCH", integer_to_list(8 * erlang:system_info(wordsize))},
+     {"ERLANG_ARCH",
+      try erlang:system_info({wordsize, external}) of
+          Val ->
+              integer_to_list(8 * Val)
+      catch
+          error:badarg ->
+              integer_to_list(8 * erlang:system_info(wordsize))
+      end},
      {"ERLANG_TARGET", rebar_utils:get_arch()},
 
      %% Solaris specific flags

src/rebar_utils.erl

@@ -62,7 +62,13 @@ is_arch(ArchRegex) ->
     end.
 
 get_arch() ->
-    Words = integer_to_list(8 * erlang:system_info(wordsize)),
+    Words = try erlang:system_info({wordsize, external}) of
+                Val ->
+                    integer_to_list(8 * Val)
+            catch
+                error:badarg ->
+                    integer_to_list(8 * erlang:system_info(wordsize))
+            end,
     erlang:system_info(otp_release) ++ "-"
         ++ erlang:system_info(system_architecture) ++ "-" ++ Words.