otherwise will report error:

  type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int [-Werror,-Wimplicit-int]

diff --git a/config/ctype.c b/config/ctype.c
index ae6ed8b..3f05677 100644
--- a/config/ctype.c
+++ b/config/ctype.c
@@ -16,4 +16,4 @@ ulong ul;
 #ifdef VK_NEED_UINT
 uint ui;
 #endif
-main(){}
+int main(){}
diff --git a/config/dl.c b/config/dl.c
index e16ff86..6db52e0 100644
--- a/config/dl.c
+++ b/config/dl.c
@@ -2,7 +2,7 @@
 /*  dl.c -- used by configure script to detect dynamic link loader            */
 /*----------------------------------------------------------------------------*/
 #include <dlfcn.h>
-main()
+int main()
 {
 	dlopen(0, 0);
 }
diff --git a/config/qc.c b/config/qc.c
index d70d10b..01def92 100644
--- a/config/qc.c
+++ b/config/qc.c
@@ -2,7 +2,7 @@
 #include <qstring.h>
 #include <qcstring.h>
 
-main()
+int main()
 {
 	for( int i=128; i<256; i++ ) {
 		char buf[4];
diff --git a/config/x.c b/config/x.c
index c5bdd8b..d35eb0a 100644
--- a/config/x.c
+++ b/config/x.c
@@ -2,6 +2,6 @@
 /*  x.c -- used by configure script to detect X lib                           */
 /*----------------------------------------------------------------------------*/
 #include <X11/Xlib.h>
-main() {
+int main() {
 	XOpenDisplay(NULL);
 }
diff --git a/config/xft.c b/config/xft.c
index ff4fc7d..148f444 100644
--- a/config/xft.c
+++ b/config/xft.c
@@ -1,6 +1,6 @@
 #include <X11/Xft/Xft.h>
 
-main()
+int main()
 {
 	XftFontOpenName(0, 0, 0);
 }