Enable by default the GCC plug-in extension

ChangeLog

@@ -18,6 +18,7 @@ StarPU 1.0 (svn revision xxxx)
 ==============================================
 The extensions-again release
 
+  * Enable by default the GCC plug-in extension.
   * Add a field named magic to struct starpu_task which is set when
         initialising the task. starpu_task_submit will fail if the
         field does not have the right value. This will hence avoid

configure.ac

@@ -1134,14 +1134,18 @@ AC_ARG_ENABLE([gcc-extensions],
   [enable_gcc_plugin="$enableval"],
   [enable_gcc_plugin="no"])
 
-if test "x$enable_gcc_plugin" = "xyes"; then
-   STARPU_GCC_PLUGIN_SUPPORT
+if test "x$enable_gcc_plugin" = "xyes" ; then
+    STARPU_GCC_PLUGIN_SUPPORT
 
-   if test "x$ac_cv_have_gcc_plugins" != "xyes"; then
-     AC_MSG_ERROR([This compiler lacks GCC plug-in support.])
-   fi
+    if test "x$ac_cv_have_gcc_plugins" != "xyes" -a "x$enable_gcc_plugin" = "xyes" ; then
+        AC_MSG_ERROR([This compiler lacks GCC plug-in support.])
+    fi
+else
+    ac_cv_have_gcc_plugins="no"
+fi
 
-   build_gcc_plugin="yes"
+if test "x$ac_cv_have_gcc_plugins" = "xyes" ; then
+    build_gcc_plugin="yes"
 
    # GNU Guile 1.8/2.0 is used to run the test suite.
    AC_PATH_PROG([GUILE], [guile])

doc/chapters/c-extensions.texi

@@ -7,11 +7,15 @@
 @cindex C extensions
 @cindex GCC plug-in
 
-When configured with @code{--enable-gcc-extensions}, 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.}.  Those extensions include syntactic sugar for defining
+If the GCC used to compile StarPU provides a plug-in
+support@footnote{This feature is only available for GCC 4.5 and
+later.}, StarPU will then build 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.
+
+The plug-in can be disabled by configuring with @code{--disable-gcc-extensions}.
+
+Those extensions include syntactic sugar for defining
 tasks and their implementations, invoking a task, and manipulating data
 buffers.  Use of these extensions can be made conditional on the
 availability of the plug-in, leading to valid C sequential code when the

doc/chapters/configuration.texi

@@ -254,6 +254,12 @@ Specify the linking flags for the MKL Library. Note that the
 @url{http://software.intel.com/en-us/articles/intel-mkl-link-line-advisor/}
 website provides a script to determine the linking flags.
 
+@node --disable-gcc-extensions
+@subsubsection @code{--enable-gcc-extensions}
+
+Disable the GCC plug-in. It is by default enabled if the GCC compiler
+provides a plug-in support.
+
 @node Execution configuration through environment variables
 @section Execution configuration through environment variables