Backup --version-script with -export-symbols-regex

When ld doesn't support --version-script, use -export-symbols-regex
instead.

configure.ac

@@ -96,7 +96,7 @@ AC_ARG_ENABLE([ld-version-script],
 
 if test "$enable_version_script" = auto
 then
-	AC_MSG_CHECKING([whether $LD supports --version-scripts. enable_version_script=$enable_version_script])
+	AC_MSG_CHECKING([whether $LD supports --version-scripts.])
 	SAVED_LDFLAGS="$LDFLAGS"
 	LDFLAGS="$LDFLAGS -Wl,--version-script=conftest.map"
 	cat > conftest.map <<EOF

src/libmdb/Makefile.am

@@ -5,4 +5,6 @@ AM_CPPFLAGS	=	-I$(top_srcdir)/include $(GLIB_CFLAGS)
 LIBS = $(GLIB_LIBS) @LIBS@
 if VERSION_SCRIPT
   libmdb_la_LDFLAGS += -Wl,--version-script=$(srcdir)/libmdb.map
+else
+  libmdb_la_LDFLAGS += -export-symbols-regex '^(mdb_|_mdb_put_int16$$|_mdb_put_int32$$)'
 endif

src/odbc/Makefile.am

@@ -9,4 +9,6 @@ LIBS	=	@LEXLIB@ $(GLIB_LIBS) $(ODBC_LIBS)
 unittest_LDADD	=	libmdbodbc.la ../libmdb/libmdb.la ../sql/libmdbsql.la
 if VERSION_SCRIPT
   libmdbodbc_la_LDFLAGS += -Wl,--version-script=$(srcdir)/libmdbodbc.map
+else
+  libmdbodbc_la_LDFLAGS += -export-symbols-regex '^(SQL|ODBCINST)'
 endif

src/sql/Makefile.am

@@ -8,4 +8,6 @@ libmdbsql_la_LIBADD =	../libmdb/libmdb.la
 YACC = @YACC@ -d
 if VERSION_SCRIPT
   libmdbsql_la_LDFLAGS += -Wl,--version-script=$(srcdir)/libmdbsql.map
+else
+  libmdbsql_la_LDFLAGS += -export-symbols-regex '^mdb_sql_'
 endif