https://github.com/royhills/ike-scan/pull/39

Before:
```
checking whether clang accepts -fstack-protector... yes
checking whether clang accepts -D_FORTIFY_SOURCE... yes
checking whether clang accepts -Wformat-security... no
```

After:
```
checking whether clang accepts -fstack-protector... yes
checking whether clang accepts -Wformat-security... yes
checking whether clang accepts -D_FORTIFY_SOURCE... yes
```

--- a/acinclude.m4
+++ b/acinclude.m4
@@ -144,7 +144,7 @@
     return 0;
   return 1;
 }
-main() {
+int main() {
   return ! does_int64_work();
 }],
 [Ac_cachevar=yes],
@@ -180,6 +180,7 @@
 AC_CACHE_VAL(pgac_cv_snprintf_long_long_int_format,
 [for pgac_format in '%lld' '%qd' '%I64d'; do
 AC_TRY_RUN([#include <stdio.h>
+#include <string.h>
 typedef long long int int64;
 #define INT64_FORMAT "$pgac_format"
 
@@ -200,7 +201,7 @@
     return 0;			/* either multiply or snprintf is busted */
   return 1;
 }
-main() {
+int main() {
   return ! does_int64_snprintf_work();
 }],
 [pgac_cv_snprintf_long_long_int_format=$pgac_format; break],
@@ -278,7 +279,7 @@
 dnl is not present on all the operating systems that we support, e.g. OpenBSD.
 dnl
 AC_DEFUN([GCC_FORTIFY_SOURCE],[
-   if test "x$CC" != "X"; then
+   if test "X$CC" != "X"; then
       AC_MSG_CHECKING([whether ${CC} accepts -D_FORTIFY_SOURCE])
       AC_TRY_COMPILE(,[
          #define GNUC_PREREQ(maj, min) ((__GNUC__ << 16) + __GNUC_MINOR__ >= ((maj) << 16) + (min))
@@ -311,7 +312,7 @@
 dnl warnings.
 dnl
 AC_DEFUN([GCC_FORMAT_SECURITY],[
-   if test "x$CC" != "X"; then
+   if test "X$CC" != "X"; then
       AC_MSG_CHECKING([whether ${CC} accepts -Wformat-security])
       wfs_old_cflags="$CFLAGS"
       CFLAGS="$CFLAGS -Wall -Werror -Wformat -Wformat-security"
--- a/configure.ac
+++ b/configure.ac
@@ -34,8 +34,8 @@
    CFLAGS="$CFLAGS -Wall -Wshadow -Wwrite-strings"
    GCC_WEXTRA
    GCC_STACK_PROTECT_CC
-   GCC_FORTIFY_SOURCE
    GCC_FORMAT_SECURITY
+   GCC_FORTIFY_SOURCE
 dnl Uncomment the lines below for testing with stricter warnings.
 dnl CFLAGS="$CFLAGS -pedantic -Wpointer-arith -Wcast-qual -Wcast-align -Wconversion -Wstrict-prototypes -Wmissing-prototypes -Wmissing-declarations -Wnested-externs -Winline "
 dnl Uncomment the line below to check malloc/free with electric fence