util: build with external libatomic

Recent versions of gcc on some architectures (MIPS, PPC, ...) moved
atomic functions into a separate library. As we are using atomic
load/store in util/time.c we may need to link libgnunetutil against
libatomic for __atomic_load_8 and __atomic_store_8 to be defined.

Fixes build problem on MIPS:
ld: ./.libs/libgnunetutil.so: undefined reference to `__atomic_store_8'
ld: ./.libs/libgnunetutil.so: undefined reference to `__atomic_load_8'
collect2: error: ld returned 1 exit status

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/configure.ac b/configure.ac
index 87a60cb04..745300939 100644
--- a/configure.ac
+++ b/configure.ac
@@ -282,6 +282,7 @@ have_addrinfo_a=0
 AC_CHECK_LIB(anl, getaddrinfo_a, [have_addrinfo_a=1 AC_DEFINE(HAVE_GETADDRINFO_A,1,[getaddrinfo_a supported])])
 AM_CONDITIONAL(HAVE_GETADDRINFO_A, [test "$have_addrinfo_a" = 1])
 
+
 # tests only run on Windows
 if test "x$build_target" = "xmingw"
 then
@@ -676,6 +677,8 @@ else
         AC_DEFINE([HAVE_LIBCURL],[1],[Have CURL])
 fi
 
+AC_SEARCH_LIBS(__atomic_load_8, atomic, [have_libatomic=1 AC_DEFINE(HAVE_LIBATOMIC,1,[external libatomic])])
+AM_CONDITIONAL(HAVE_LIBATOMIC, [test "$have_libatomic" = 1])
 
 # restore LIBS & CPPFLAGS
 LIBS=$SAVE_LIBS