Clarify docs for common macros

Numeric macros such as MIN(), MAX(), etc. should not be handed
arguments with side-effects, such as i++, since we can't guarantee
that the values are only evaluated once.

glib/docs.c

@@ -946,6 +946,8 @@
  *
  * Calculates the minimum of @a and @b.
  *
+ * Note that it is an error to pass values with side-effects.
+ *
  * Returns: the minimum of @a and @b.
  */
 
@@ -956,6 +958,8 @@
  *
  * Calculates the maximum of @a and @b.
  *
+ * Note that it is an error to pass values with side-effects.
+ *
  * Returns: the maximum of @a and @b.
  */
 
@@ -970,6 +974,8 @@
  * - ABS(-10) is 10.
  * - ABS(10) is also 10.
  *
+ * Note that it is an error to pass values with side-effects.
+ *
  * Returns: the absolute value of @a.
  */
 
@@ -987,6 +993,8 @@
  * - CLAMP(15, 5, 10) is 10.
  * - CLAMP(20, 15, 25) is 20.
  *
+ * Note that it is an error to pass values with side-effects.
+ *
  * Returns: the value of @x clamped to the range between @low and @high
  */
 
@@ -1005,6 +1013,8 @@
  * - `G_APPROX_VALUE (n, 0.f, FLT_EPSILON)` evaluates to true if `n` is within
  *   the single precision floating point epsilon from zero
  *
+ * Note that it is an error to pass values with side-effects.
+ *
  * Returns: %TRUE if the two values are within the desired range
  *
  * Since: 2.58