configure.ac: Add HAVE_OPENCL AM_CONDITIONAL v2

v2:
  - Drop HAVE_OPENCL variable for non-automake builds
  - s/HAVE_OPENCL/HAVE_GALLIUM_COMPUTE

Reviewed-by: Francisco Jerez <currojerez@riseup.net>
diff --git a/configure.ac b/configure.ac
index 9fb8149..06fc2de 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2080,6 +2080,7 @@
 AM_CONDITIONAL(USE_R600_LLVM_COMPILER, test x$USE_R600_LLVM_COMPILER = xyes)
 AM_CONDITIONAL(HAVE_LOADER_GALLIUM, test x$enable_gallium_loader = xyes)
 AM_CONDITIONAL(HAVE_DRM_LOADER_GALLIUM, test x$enable_gallium_drm_loader = xyes)
+AM_CONDITIONAL(HAVE_GALLIUM_COMPUTE, test x$enable_opencl = xyes)
 AC_SUBST([GALLIUM_MAKE_DIRS])
 
 AM_CONDITIONAL(HAVE_X11_DRIVER, echo "$DRIVER_DIRS" | grep 'x11' >/dev/null 2>&1)