[gimp] app: build layer mode operations with SSE2 flags.

[Jehan Pagès <jehanp src gnome org>]

commit e957347dd693d8e2a96e5ed194a4136d50fae976
Author: Jehan <jehan girinstud io>
Date:   Thu Feb 2 21:20:54 2017 +0100

    app: build layer mode operations with SSE2 flags.
    
    Some of the generic files still contain SSE2 code, in particular
    gimpoperationlayermode.c. The reason why it often works without is that
    native gcc will usually pre-define SSE macros by default.
    To check this: gcc -dM -E - < /dev/null | grep SSE
    Yet I had a case on a small netbook where the SSE macros were not
    pre-defined even though supported. Consequently the build failed.

 app/operations/layer-modes/Makefile.am |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/app/operations/layer-modes/Makefile.am b/app/operations/layer-modes/Makefile.am
index 6aa9063..2764580 100644
--- a/app/operations/layer-modes/Makefile.am
+++ b/app/operations/layer-modes/Makefile.am
@@ -9,6 +9,7 @@ AM_CPPFLAGS = \
        $(CAIRO_CFLAGS)                         \
        $(GEGL_CFLAGS)                          \
        $(GDK_PIXBUF_CFLAGS)                    \
+       $(SSE2_EXTRA_CFLAGS)            \
        -I$(includedir)
 
 noinst_LIBRARIES = \