gcc-plugin: honor `--tag' libtool flag.

gcc-plugin/src/Makefile.am (AM_LDFLAGS): move `--tag=...' to...
(AM_LIBTOOLFLAGS): ...here so that it is honored by libtool. This
should fix linking issues starting with GCC 4.7.

gcc-plugin/src/Makefile.am

@@ -28,10 +28,11 @@ AM_CPPFLAGS =						\
   -I$(GCC_PLUGIN_INCLUDE_DIR) -Wall -DYYERROR_VERBOSE=1 \
   $(STARPU_CUDA_CPPFLAGS) $(STARPU_OPENCL_CPPFLAGS)
 
-AM_LDFLAGS = -module --tag="$(GCC_FOR_PLUGIN_LIBTOOL_TAG)"
+AM_LDFLAGS = -module
 
 # Use either `gcc' or `g++', whichever is appropriate to build
 # plug-ins for this version of GCC.
+AM_LIBTOOLFLAGS = --tag="$(GCC_FOR_PLUGIN_LIBTOOL_TAG)"
 CC = $(GCC_FOR_PLUGIN)
 
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