Remove unsupported -Wtype-limits for GCC < 4.3.5 (closes #109)

configure.ac

@@ -111,12 +111,13 @@ AC_CHECK_DECLS([TIOCSRS485], [], [], [[#include <sys/ioctl.h>]])
 # Check for RTS flags
 AC_CHECK_DECLS([TIOCM_RTS], [], [], [[#include <sys/ioctl.h>]])
 
+# Wtype-limits is not supported by gcc 4.2 (default on recent Mac OS X)
 my_CFLAGS="-Wall \
 -Wmissing-declarations -Wmissing-prototypes \
 -Wnested-externs -Wpointer-arith \
 -Wpointer-arith -Wsign-compare -Wchar-subscripts \
 -Wstrict-prototypes -Wshadow \
--Wformat-security -Wtype-limits"
+-Wformat-security"
 AC_SUBST([my_CFLAGS])
 
 AC_CONFIG_HEADERS([config.h tests/unit-test.h])