Fix building on Cygwin

Achim reported that 2.10.0 no longer builds on Cygwin, while 2.9.4 did.
This was magnificently obscure, at least to this Unix-head.  Initially
it appeared to be an issue with inter-library linking between libman and
libmandb, but 2.9.4 relied on that too, just slightly less so.

The actual problem was that libman only exported
`gl_get_setlocale_null_lock` and not all the other symbols it's supposed
to export, which is because that was explicitly marked for export and no
other symbols were.  Building libman with `-Wl,--export-all-symbols`
fixes this; libman is intended as an aggregation of various helper
functions, including those from Gnulib, and it doesn't make sense to be
especially selective since it's only installed as a private library
anyway.

(I'm still not exactly sure why 2.9.4 didn't do the same thing, but this
seems to be a good enough fix.)

* configure.ac: Set LIBMAN_EXPORT_LDFLAGS to '-Wl,--export-all-symbols'
when linking with GNU ld on Windows platforms.
* lib/Makefile.am (libman_la_LDFLAGS): Add $(LIBMAN_EXPORT_LDFLAGS).
* src/Makefile.am (LIBMAN): Remove $(top_builddir)/gl/lib/libgnu.la; as
a convenience library, this is already incorporated into libman.la, and
specifying it again causes multiple-definition errors on Cygwin.
* src/tests/Makefile.am (get_mtime_LDADD): Likewise.
* NEWS.md: Document this.

5 files changed, 15 insertions, 5 deletions

diff --git a/NEWS.md b/NEWS.md
index 9bb61343..f39603b1 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -7,6 +7,7 @@ Fixes:
  * Fix inadvertent reliance on a GCC extension that caused build failures
    with Clang.
  * Fix building without `iconv`.
+ * Fix building on Cygwin.
 
 man-db 2.10.0 (4 February 2022)
 ===============================
diff --git a/configure.ac b/configure.ac
index f3f47be5..7748edd2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -97,6 +97,17 @@ AC_PROG_INSTALL
 AC_PROG_LN_S
 AM_PROG_AR
 LT_INIT([disable-static])
+
+libman_export_ldflags=
+if test "$with_gnu_ld" = yes; then
+	case $host_os in
+		cygwin*|mingw*|pw32*|cegcc*)
+			libman_export_ldflags='-Wl,--export-all-symbols'
+			;;
+	esac
+fi
+AC_SUBST([LIBMAN_EXPORT_LDFLAGS], [$libman_export_ldflags])
+
 AC_CHECK_PROGS([cat], [cat])
 AC_DEFINE_UNQUOTED([PROG_CAT], ["$cat"], [Program to use as cat.])
 MAN_CHECK_PROGS([browser], [BROWSER], [use BROWSER as default web browser], [www-browser lynx elinks w3m])
diff --git a/lib/Makefile.am b/lib/Makefile.am
index 475fea04..49f7809f 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -70,4 +70,5 @@ libman_la_LIBADD = ../gl/lib/libgnu.la $(LTLIBOBJS) \
 libman_la_LDFLAGS = \
 	-avoid-version -release $(VERSION) -rpath $(pkglibdir) \
 	-no-undefined \
+	$(LIBMAN_EXPORT_LDFLAGS) \
 	$(libseccomp_LIBS)
diff --git a/src/Makefile.am b/src/Makefile.am
index e55cdda2..7d4a398b 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -56,8 +56,7 @@ AM_CFLAGS = \
 	$(WARN_CFLAGS) \
 	$(libpipeline_CFLAGS)
 
-LIBMAN = $(top_builddir)/lib/libman.la $(top_builddir)/gl/lib/libgnu.la \
-	 @LTLIBINTL@
+LIBMAN = $(top_builddir)/lib/libman.la @LTLIBINTL@
 LIBMANDB = $(top_builddir)/libdb/libmandb.la $(LIBMAN) $(DBLIBS)
 
 accessdb_LDADD = $(LIBMANDB)
diff --git a/src/tests/Makefile.am b/src/tests/Makefile.am
index 35aa20f8..6491417b 100644
--- a/src/tests/Makefile.am
+++ b/src/tests/Makefile.am
@@ -74,8 +74,6 @@ fspause_LDADD = \
 	$(top_builddir)/gl/lib/libgnu.la \
 	$(LIB_NANOSLEEP)
 get_mtime_SOURCES = get-mtime.c
-get_mtime_LDADD = \
-	$(top_builddir)/lib/libman.la \
-	$(top_builddir)/gl/lib/libgnu.la
+get_mtime_LDADD = $(top_builddir)/lib/libman.la
 
 dist_check_SCRIPTS = testlib.sh $(ALL_TESTS)