macros: add G_GNUC_CHECK_VERSION() for compiler checks.

https://bugzilla.gnome.org/show_bug.cgi?id=728099

docs/reference/glib/glib-sections.txt

@@ -407,6 +407,7 @@ G_STATIC_ASSERT
 G_STATIC_ASSERT_EXPR
 
 <SUBSECTION>
+G_GNUC_CHECK_VERSION
 G_GNUC_EXTENSION
 G_GNUC_CONST
 G_GNUC_PURE

glib/docs.c

@@ -1995,6 +1995,21 @@
  * with the `-pedantic` option.
  */
 
+/**
+ * G_GNUC_CHECK_VERSION:
+ *
+ * Expands to a a check for a compiler with __GNUC__ defined and a version
+ * greater than or equal to the major and minor numbers provided. For example,
+ * the following would only match on compilers such as GCC 4.8 or newer.
+ *
+ * |[<!-- language="C" -->
+ * #if G_GNUC_CHECK_VERSION(4, 8)
+ * #endif
+ * ]|
+ *
+ * Since: 2.42
+ */
+
 /**
  * G_GNUC_CONST:
  *

glib/gmacros.h

@@ -37,6 +37,12 @@
  */
 #include <stddef.h>
 
+#define G_GNUC_CHECK_VERSION(major, minor) \
+    (defined(__GNUC__) && \
+     ((__GNUC__ > (major)) || \
+      ((__GNUC__ == (major)) && \
+       (__GNUC_MINOR__ >= (minor)))))
+
 /* Here we provide G_GNUC_EXTENSION as an alias for __extension__,
  * where this is valid. This allows for warningless compilation of
  * "long long" types even in the presence of '-ansi -pedantic'.