Revert "configure: allow checking multiple functions in check_func_headers()"

This reverts commit edaf1ae2.

breaks windows builds

configure

@@ -700,17 +700,20 @@ EOF
 check_func_headers(){
     log check_func_headers "$@"
     headers=$1
-    funcs=$2
+    func=$2
     shift 2
-    {
-        for hdr in $headers; do
-            echo "#include <$hdr>"
-        done
-        for func in $funcs; do
-            echo "long check_$func(void) { return (long) $func; }"
-        done
-        echo "int main(void) { return 0; }"
-    } | check_ld "$@" && enable $funcs && enable_safe $headers
+    disable $func
+    incs=""
+    for hdr in $headers; do
+        incs="$incs
+#include <$hdr>"
+    done
+    check_ld "$@" <<EOF && enable $func && enable_safe $headers
+$incs
+int main(int argc, char **argv){
+    return (long) $func;
+}
+EOF
 }
 
 check_cpp_condition(){
@@ -737,9 +740,9 @@ check_lib(){
 check_lib2(){
     log check_lib2 "$@"
     headers="$1"
-    funcs="$2"
+    func="$2"
     shift 2
-    check_func_headers "$headers" "$funcs" "$@" && add_extralibs "$@"
+    check_func_headers "$headers" $func "$@" && add_extralibs "$@"
 }
 
 check_exec(){