Add G_GNUC_BEGIN/END_IGNORE_DEPRECATIONS

Add new macros to disable -Wdeprecated-declarations around a piece of
code, using the C99 (and GNU89) _Pragma() operator. Replace the
existing use of #pragma for this in gio, and suppress the warnings in
gvaluearray.c as well.

https://bugzilla.gnome.org/show_bug.cgi?id=669671

glib/docs.c

@@ -1986,6 +1986,39 @@
  * Since: 2.26
  */
 
+/**
+ * G_GNUC_BEGIN_IGNORE_DEPRECATIONS:
+ *
+ * Tells <command>gcc</command> (if it is a new enough version) to
+ * temporarily stop emitting warnings when functions marked with
+ * %G_GNUC_DEPRECATED or %G_GNUC_DEPRECATED_FOR are called. This is
+ * useful for when you have one deprecated function calling another
+ * one, or when you still have regression tests for deprecated
+ * functions.
+ *
+ * Use %G_GNUC_END_IGNORE_DEPRECATIONS to begin warning again. (If you
+ * are not compiling with <literal>-Wdeprecated-declarations</literal>
+ * then neither macro has any effect.)
+ *
+ * This macro can be used either inside or outside of a function body,
+ * but must appear on a line by itself.
+ *
+ * Since: 2.32
+ */
+
+/**
+ * G_GNUC_END_IGNORE_DEPRECATIONS:
+ *
+ * Undoes the effect of %G_GNUC_BEGIN_IGNORE_DEPRECATIONS, telling
+ * <command>gcc</command> to begin outputting warnings again
+ * (assuming those warnings had been enabled to begin with).
+ *
+ * This macro can be used either inside or outside of a function body,
+ * but must appear on a line by itself.
+ *
+ * Since: 2.32
+ */
+
 /**
  * G_GNUC_NORETURN:
  *