tests/opt/Makefile.am: add $(top_builddir)/src as include directory

tests/opt/Makefile.am

@@ -17,7 +17,7 @@
 
 AM_CFLAGS = $(HWLOC_CFLAGS) -Wall $(STARPU_CUDA_CPPFLAGS) $(STARPU_OPENCL_CPPFLAGS)
 LIBS = $(top_builddir)/src/libstarpu-@STARPU_EFFECTIVE_VERSION@.la $(HWLOC_LIBS) @LIBS@
-AM_CPPFLAGS = -I$(top_srcdir)/include/ -I$(top_srcdir)/src/
+AM_CPPFLAGS = -I$(top_srcdir)/include/ -I$(top_srcdir)/src/ -I$(top_builddir)/src
 AM_LDFLAGS = $(STARPU_CUDA_LDFLAGS) $(STARPU_OPENCL_LDFLAGS)
 
 optbindir = $(libdir)/starpu/tests