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, 3 insertions, 2 deletions

diff --git a/erts/emulator/drivers/common/gzio.c b/erts/emulator/drivers/common/gzio.c
index ca6d25adb4..e085c262b0 100644
--- a/erts/emulator/drivers/common/gzio.c
+++ b/erts/emulator/drivers/common/gzio.c
@@ -13,6 +13,7 @@
 #  include "config.h"
 #endif
 #include <stdio.h>
+#include <string.h> /* ssize_t on Mac OS X */
 #include <errno.h>
 #ifdef HAVE_UNISTD_H
 #include <unistd.h>
@@ -314,7 +315,7 @@ local int get_byte(s)
     if (s->z_eof) return EOF;
     if (s->stream.avail_in == 0) {
 #ifdef UNIX
-	size_t res;
+	ssize_t res;
 	errno = 0;
 	res = ERTS_GZREAD(s->file, s->inbuf, Z_BUFSIZE);
 	if (res == 0) {
@@ -487,7 +488,7 @@ erts_gzread(gzFile file, voidp buf, unsigned len)
 	}
         if (s->stream.avail_in == 0 && !s->z_eof) {
 #ifdef UNIX
-	    size_t res;
+	    ssize_t res;
 	    errno = 0;
 	    res = ERTS_GZREAD(s->file, s->inbuf, Z_BUFSIZE);
 	    if (res == 0) {