Fix a regression in glibc 2.27 when built without ldconfig.  See
<https://sourceware.org/bugzilla/show_bug.cgi?id=22977> for details.

diff --git a/include/libc-symbols.h b/include/libc-symbols.h
index 6137304b0b..7d630f36d8 100644
--- a/include/libc-symbols.h
+++ b/include/libc-symbols.h
@@ -508,7 +508,7 @@ for linking")
 # ifndef __ASSEMBLER__
 #  if !defined SHARED && IS_IN (libc) && !defined LIBC_NONSHARED \
       && (!defined PIC || !defined NO_HIDDEN_EXTERN_FUNC_IN_PIE) \
-      && !defined NO_HIDDEN
+      && !defined NO_HIDDEN && defined USE_LDCONFIG
 #   define __hidden_proto_hiddenattr(attrs...) \
   __attribute__ ((visibility ("hidden"), ##attrs))
 #   define hidden_proto(name, attrs...) \
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<tr><td><span title='2016-05-04 23:35:55 +0200'>2016-05-04</span></td><td><a href='/guix/commit/tests/combinators.scm?id=958dd3ce68733bcd5c1231424c7e4ad39e67594a'>utils: Move combinators to (guix combinators).</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/utils.scm (compile-time-value, memoize, fold2)
(fold-tree, fold-tree-leaves): Move to...
* guix/combinators: ... here.  New file.
* tests/utils.scm ("fold2, 1 list", "fold2, 2 lists")
(fold-tree tests): Move to...
* tests/combinators.scm: ... here.  New file.
* Makefile.am (MODULES, SCM_TESTS): Add them.
* gnu/packages.scm, gnu/packages/bootstrap.scm,
gnu/services/herd.scm, guix/build-system/gnu.scm,
guix/build-system/python.scm, guix/derivations.scm,
guix/gnu-maintenance.scm, guix/import/elpa.scm,
guix/scripts/archive.scm, guix/scripts/build.scm,
guix/scripts/graph.scm, guix/scripts/lint.scm,
guix/scripts/size.scm, guix/scripts/substitute.scm,
guix/serialization.scm, guix/store.scm, guix/ui.scm: Adjust imports
accordingly.
</span></span></td><td>Ludovic Courtès</td></tr>