Fix clang compiler warnings on FreeBSD in erts

The following are deliberately left, as I have only a list of compiler
warnings and no system to test on:
hipe/hipe_x86_signal.c:264:5: warning: no previous prototype for function '_sigaction' [-Wmissing-prototypes]
int __SIGACTION(int signum, const struct sigaction *act, struct sigaction *oldact)
    ^
hipe/hipe_x86_signal.c:222:21: note: expanded from macro '__SIGACTION'
                    ^
1 warning generated.
sys/unix/sys_float.c:835:16: warning: declaration of 'struct exception' will not be visible outside of this function [-Wvisibility]
matherr(struct exception *exc)
               ^
sys/unix/sys_float.c:835:1: warning: no previous prototype for function 'matherr' [-Wmissing-prototypes]
matherr(struct exception *exc)
^
2 warnings generated.
drivers/unix/unix_efile.c:1504:11: warning: implicit declaration of function 'sendfile' [-Wimplicit-function-declaration]
        retval = sendfile(in_fd, out_fd, *offset, SENDFILE_CHUNK_SIZE,
                 ^
1 warning generated.

1 files changed, 2 insertions, 2 deletions

diff --git a/erts/emulator/beam/external.c b/erts/emulator/beam/external.c
index ab1065aaa1..126f242fc0 100644
--- a/erts/emulator/beam/external.c
+++ b/erts/emulator/beam/external.c
@@ -926,7 +926,7 @@ BIF_RETTYPE erts_debug_dist_ext_to_term_2(BIF_ALIST_2)
     Eterm res;
     Eterm *hp;
     Eterm *hendp;
-    Uint hsz;
+    Sint hsz;
     ErtsDistExternal ede;
     Eterm *tp;
     Eterm real_bin;
@@ -972,7 +972,7 @@ BIF_RETTYPE erts_debug_dist_ext_to_term_2(BIF_ALIST_2)
     if (hsz < 0)
 	goto badarg;
 
-    hp = HAlloc(BIF_P, hsz);
+    hp = HAlloc(BIF_P, (Uint) hsz);
     hendp = hp + hsz;
 
     res = erts_decode_dist_ext(&hp, &MSO(BIF_P), &ede);