CLEANUP: compat: make the MIN/MAX macros more reliable

After every release we say that MIN/MAX should be changed to be an
expression that only evaluates each operand once, and before every
version we forget to change it and we recheck that the code doesn't
misuse them. Let's fix them now.

include/haproxy/compat.h

@@ -94,11 +94,19 @@ typedef struct { } empty_t;
 #endif
 
 #ifndef MIN
-#define MIN(a, b) (((a) < (b)) ? (a) : (b))
+#define MIN(a, b) ({				\
+	typeof(a) _a = (a);			\
+	typeof(a) _b = (b);			\
+	((_a < _b) ? _a : _b);			\
+})
 #endif
 
 #ifndef MAX
-#define MAX(a, b) (((a) > (b)) ? (a) : (b))
+#define MAX(a, b) ({				\
+	typeof(a) _a = (a);			\
+	typeof(a) _b = (b);			\
+	((_a > _b) ? _a : _b);			\
+})
 #endif
 
 /* this is for libc5 for example */