doc: Mention GCC 4.7 support.

* doc/chapters/c-extensions.texi: List supported GCC versions.

doc/chapters/c-extensions.texi

@@ -10,7 +10,8 @@
 When GCC plug-in support is available, StarPU builds a plug-in for the
 GNU Compiler Collection (GCC), which defines extensions to languages of
 the C family (C, C++, Objective-C) that make it easier to write StarPU
-code@footnote{This feature is only available for GCC 4.5 and later.  You
+code@footnote{This feature is only available for GCC 4.5 and later; it
+is known to work with GCC 4.5, 4.6, and 4.7.  You
 may need to install a specific @code{-dev} package of your distro, such
 as @code{gcc-4.6-plugin-dev} on Debian and derivatives.  In addition,
 the plug-in's test suite is only run when