build: don't fail if linker version scripts are not supported

Some platforms (such as OSX) do not support version scripts. In these
platforms the symbols will not be versioned, but it is OK to omit them.

#24

Makefile.am

@@ -97,7 +97,9 @@ libxkbcommon_la_SOURCES = \
 	src/utf8.h \
 	src/utils.c \
 	src/utils.h
+if HAVE_VERSION_SCRIPT
 libxkbcommon_la_LDFLAGS = -Wl,--version-script=${srcdir}/xkbcommon.map
+endif HAVE_VERSION_SCRIPT
 
 if ENABLE_X11
 pkgconfig_DATA += xkbcommon-x11.pc
@@ -111,7 +113,9 @@ lib_LTLIBRARIES += libxkbcommon-x11.la
 libxkbcommon_x11_la_CFLAGS = $(AM_CFLAGS) $(XCB_XKB_CFLAGS)
 libxkbcommon_x11_la_CPPFLAGS = $(AM_CPPFLAGS) -I$(top_srcdir)/src/x11
 libxkbcommon_x11_la_LIBADD = libxkbcommon.la $(XCB_XKB_LIBS)
+if HAVE_VERSION_SCRIPT
 libxkbcommon_x11_la_LDFLAGS = -Wl,--version-script=${srcdir}/xkbcommon-x11.map
+endif HAVE_VERSION_SCRIPT
 
 libxkbcommon_x11_la_SOURCES = \
 	src/x11/keymap.c \

configure.ac

@@ -100,9 +100,11 @@ openbsd*)
 *)
     XORG_CHECK_LINKER_FLAGS([-Wl,--no-undefined], [have_no_undefined=yes]) ;;
 esac
-
 AM_CONDITIONAL([HAVE_NO_UNDEFINED], [test "x$have_no_undefined" = xyes])
 
+XORG_CHECK_LINKER_FLAGS([-Wl,--version-script="$srcdir/xkbcommon.map"], [have_version_script=yes])
+AM_CONDITIONAL([HAVE_VERSION_SCRIPT], [test "x$have_version_script" = xyes])
+
 AC_CHECK_LIB(rt, clock_gettime,
     [AC_SUBST(RT_LIBS, "-lrt")],
     [AC_SUBST(RT_LIBS, "")],