Avoid configure checks being optimized away with LTO

In case the checks are compiled with CFLAGS including "-O1 -flto" (or any
other optimization level), a "test()" function not referenced by by main
will be optimized away and discarded prior to the final linking step, and
there will be no undefined symbols, thus the checks always succeeds.

This at least affects the "strlcpy"/"strlcat" checks, but may affects other
checks as well.

diff --git a/configure b/configure
index e5f6f593b673d8c91ecc9bba726afd64ee4decf1..e76760479a947102cfb68257b15d3819528ef2d2 100755 (executable)
--- a/configure
+++ b/configure
@@ -177,27 +177,31 @@ else
 fi
 
 check_cc_snippet strlcat '#include <string.h>
-int test(int argc, char **argv) {
+#define TEST test
+int test() {
   char dst[10];
   strlcat("test", dst, sizeof(dst));
   return 0;
 }'
 
 check_cc_snippet strlcpy '#include <string.h>
-int test(int argc, char **argv) {
+#define TEST test
+int test() {
   char dst[10];
   strlcpy("test", dst, sizeof(dst));
   return 0;
 }'
 
 check_cc_snippet fdatasync '#include <unistd.h>
-int test(int argc, char **argv) {
+#define TEST test
+int test() {
   fdatasync(0);
   return 0;
 }'
 
 check_cc_snippet getloadavg '#include <stdlib.h>
-void test() { getloadavg(NULL,0); }'
+#define TEST test
+int test() { return getloadavg(NULL,0); }'
 
 check_cc_snippet atomic32 '#include <stdint.h>
 int test(int *ptr){
@@ -222,6 +226,7 @@ return __sync_fetch_and_add(ptr, (void *)1);
 }'
 
 check_cc_snippet bitops64 '#include <stdint.h>
+#define TEST test
 int test(void){
   int l = sizeof(long);
   return l == 8 ? 0 : 1;
@@ -312,6 +317,7 @@ int test(void)
 # note that iconv routines are mandatory
 check_cc_snippet libiconv '
 #include <iconv.h>
+#define TEST test
 int test(void)
 {
   iconv_t ic = iconv_open("ASCII", "ASCII");
@@ -327,6 +333,7 @@ fi
 
 check_cc_snippet ifnames '
 #include <net/if.h>
+#define TEST test
 int test(void)
 {
   struct if_nameindex *ifnames = if_nameindex();
@@ -336,6 +343,7 @@ int test(void)
 '
 
 check_cc_snippet cclang_threadsan '
+#define TEST test
 int test(void){
 #if __has_feature(thread_sanitizer)
   return 0;