build: add Valgrind suppression file for GNU/Linux

* build-aux/linux-gnu.valgrind: New.
* build-aux/local.mk: Ship it.
* configure.ac: Use it.

build-aux/linux-gnu.valgrind

@@ -0,0 +1,16 @@
+# Linux seattle 2.6.32-5-amd64 #1 SMP Thu Mar 22 17:26:33 UTC 2012
+# x86_64 GNU/Linux
+{
+   index
+   Memcheck:Cond
+   fun:index
+   fun:expand_dynamic_string_token
+   fun:_dl_map_object
+   fun:map_doit
+   fun:_dl_catch_error
+   fun:do_preload
+   fun:dl_main
+   fun:_dl_sysdep_start
+   fun:_dl_start
+   obj:/lib/ld-2.11.3.so
+}

build-aux/local.mk

@@ -16,6 +16,7 @@
 EXTRA_DIST +=                                   \
   build-aux/cross-options.pl                    \
   build-aux/darwin11.4.0.valgrind               \
+  build-aux/linux-gnu.valgrind                  \
   build-aux/move-if-change                      \
   build-aux/prev-version.txt                    \
   build-aux/update-b4-copyright