socl: do not hardcode -Wall and -Wextra in Makefile, let configure detect them and comment out call to unexisting macro STARPU_SOCL_SUPPORT

configure.ac

@@ -1169,7 +1169,7 @@ AC_ARG_ENABLE([socl],
   [enable_socl="no"])
 
 if test "x$enable_socl" = "xyes"; then
-   STARPU_SOCL_SUPPORT
+   #STARPU_SOCL_SUPPORT
    build_socl="yes"
 else
    build_socl="no"

socl/src/Makefile.am

@@ -14,7 +14,7 @@
 #
 # See the GNU Lesser General Public License in COPYING.LGPL for more details.
 
-AM_CFLAGS = -Wall -Wextra $(STARPU_CUDA_CPPFLAGS) $(STARPU_OPENCL_CPPFLAGS)
+AM_CFLAGS = $(GLOBAL_AM_CFLAGS) $(STARPU_CUDA_CPPFLAGS) $(STARPU_OPENCL_CPPFLAGS)
 LIBS = $(top_builddir)/src/libstarpu-@STARPU_EFFECTIVE_VERSION@.la
 AM_CPPFLAGS = -I$(top_srcdir)/include/ -I$(top_builddir)/include
 AM_LDFLAGS = $(STARPU_CUDA_LDFLAGS) $(STARPU_OPENCL_LDFLAGS)