Add lose const warnings test

misc/lose_const_warnings.c

@@ -0,0 +1,42 @@
+/*
+ *  Doing a cost-to-non-const cast without warnings, and without portability
+ *  or compiler specific issues is a bit challenging.
+ *
+ *  $ gcc -o/tmp/test -std=c99 -Wall -Wextra -Wcast-qual misc/lose_const_warnings.c -lm
+ *  misc/lose_const_warnings.c: In function ‘main’:
+ *  misc/lose_const_warnings.c:24:7: warning: cast discards ‘__attribute__((const))’ qualifier from pointer target type [-Wcast-qual]
+  p1 = (void *) p2;
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+typedef union {
+	void *x;
+	const void *y;
+} lose_const;
+
+int main(int argc, char *argv[]) {
+	void *p1;
+	const void *p2;
+	lose_const lc;
+
+	(void) argc; (void) argv;
+
+	/* Warning with gcc -Wcast-qual */
+	p2 = (const void *) 0xdeadbeef;
+	p1 = (void *) p2;	
+	printf("p1=%p\n", p1);
+
+	/* No warning with gcc -Wcast-qual, but (u)intptr_t types are optional */
+	p2 = (const void *) 0xdeadbeef;
+	p1 = (void *) (uintptr_t) p2;	
+	printf("p1=%p\n", p1);
+
+	/* No warning with gcc -Wcast-qual doesn't rely on optional types */
+	p2 = (const void *) 0xdeadbeef;
+	lc.y = p2;
+	p1 = lc.x;
+	printf("p1=%p\n", p1);
+}