Silence MSVC C4255 warnings.

MSVC 4255 warning:
'function' : no function prototype given: converting '()' to '(void)'

tests/general/depth_clamp.c

@@ -56,7 +56,7 @@ static GLboolean Automatic = GL_FALSE;
 #define WIN_HEIGHT 150
 
 static void
-init()
+init(void)
 {
 	glewInit();
 	piglit_require_extension("GL_ARB_depth_clamp");
@@ -72,7 +72,7 @@ init()
 }
 
 static void
-display()
+display(void)
 {
 	GLboolean pass = GL_TRUE;
 	float white[3] = {1.0, 1.0, 1.0};

tests/general/draw-elements-base-vertex.c

@@ -75,7 +75,7 @@ static GLboolean Automatic = GL_FALSE;
 static GLuint ib_offset;
 
 static void
-init()
+init(void)
 {
 	GLfloat *vb;
 	GLuint *ib;
@@ -130,7 +130,7 @@ init()
 }
 
 static void
-display()
+display(void)
 {
 	GLboolean pass = GL_TRUE;
 	float white[3] = {1.0, 1.0, 1.0};

tests/shaders/glsl-fs-fragcoord.c

@@ -83,7 +83,7 @@ display(void)
 		piglit_report_result(pass ? PIGLIT_SUCCESS : PIGLIT_FAILURE);
 }
 
-static void init()
+static void init(void)
 {
 	GLint vs, fs;