Only in curl-serenity/: config.log
diff -ru curl-7.65.3/config.sub curl-serenity/config.sub
--- curl-7.65.3/config.sub	2019-07-19 00:41:42.000000000 +0200
+++ curl-serenity/config.sub	2019-08-29 11:03:53.901037128 +0200
@@ -1364,6 +1364,7 @@
 	# Each alternative MUST end in a * to match a version number.
 	# -sysv* is not here because it comes later, after sysvr4.
 	-gnu* | -bsd* | -mach* | -minix* | -genix* | -ultrix* | -irix* \
+	      | -serenity* \
 	      | -*vms* | -sco* | -esix* | -isc* | -aix* | -cnk* | -sunos | -sunos[34]*\
 	      | -hpux* | -unos* | -osf* | -luna* | -dgux* | -auroraux* | -solaris* \
 	      | -sym* | -kopensolaris* | -plan9* \
diff -ru curl-7.65.3/configure curl-serenity/configure
--- curl-7.65.3/configure	2019-07-19 00:41:41.000000000 +0200
+++ curl-serenity/configure	2019-08-29 11:06:24.076073666 +0200
@@ -18181,51 +18181,6 @@
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 
-
-    { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler halts on function prototype mismatch" >&5
-$as_echo_n "checking if compiler halts on function prototype mismatch... " >&6; }
-  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-
-
-#     include <stdlib.h>
-      int rand(int n);
-      int rand(int n)
-      {
-        if(n)
-          return ++n;
-        else
-          return n;
-      }
-
-int main (void)
-{
-
-      int i[2]={0,0};
-      int j = rand(i[0]);
-      if(j)
-        return j;
-
- ;
- return 0;
-}
-
-_ACEOF
-if ac_fn_c_try_compile "$LINENO"; then :
-
-    { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
-$as_echo "no" >&6; }
-    as_fn_error $? "compiler does not halt on function prototype mismatch." "$LINENO" 5
-
-else
-
-    { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
-$as_echo "yes" >&6; }
-
-fi
-rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
-
-
       { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler supports hiding library internal symbols" >&5
 $as_echo_n "checking if compiler supports hiding library internal symbols... " >&6; }
   supports_symbol_hiding="no"
diff -ru curl-7.65.3/configure.ac curl-serenity/configure.ac
--- curl-7.65.3/configure.ac	2019-07-16 12:24:31.000000000 +0200
+++ curl-serenity/configure.ac	2019-08-29 11:05:47.679343943 +0200
@@ -287,7 +287,6 @@
 
 CURL_CHECK_COMPILER_HALT_ON_ERROR
 CURL_CHECK_COMPILER_ARRAY_SIZE_NEGATIVE
-CURL_CHECK_COMPILER_PROTOTYPE_MISMATCH
 CURL_CHECK_COMPILER_SYMBOL_HIDING
 
 CURL_CHECK_CURLDEBUG
diff -ru curl-7.65.3/include/curl/curl.h curl-serenity/include/curl/curl.h
--- curl-7.65.3/include/curl/curl.h	2019-07-19 00:23:35.000000000 +0200
+++ curl-serenity/include/curl/curl.h	2019-08-29 11:10:37.863071640 +0200
@@ -75,6 +75,7 @@
     defined(__minix) || defined(__SYMBIAN32__) || defined(__INTEGRITY) || \
     defined(ANDROID) || defined(__ANDROID__) || defined(__OpenBSD__) || \
     defined(__CYGWIN__) || \
+    defined(__serenity__) || \
    (defined(__FreeBSD_version) && (__FreeBSD_version < 800000))
 #include <sys/select.h>
 #endif