macros: don't use __externally_visible__ attribute for clang

clang does not support externally_visible:

    ../libnm/nm-access-point.c:243:1: error: unknown attribute externally_visible ignored [-Werror,-Wunknown-attributes]
    NM_BACKPORT_SYMBOL (libnm_1_0_6, int, nm_access_point_get_last_seen, (NMAccessPoint *ap), (ap));
    ^
    ../shared/nm-utils/nm-macros-internal.h:1299:74: note: expanded from macro NM_BACKPORT_SYMBOL
    #define NM_BACKPORT_SYMBOL(version, return_type, func, args_typed, args) \
                                                                             ^
    ../shared/nm-utils/nm-macros-internal.h:1292:17: note: expanded from macro _NM_BACKPORT_SYMBOL_IMPL
    __attribute__ ((externally_visible)) return_type versioned_func args_typed \
                    ^

1 files changed, 13 insertions, 1 deletions

diff --git a/shared/nm-utils/nm-macros-internal.h b/shared/nm-utils/nm-macros-internal.h
index 3537b37d50..55cdd374da 100644
--- a/shared/nm-utils/nm-macros-internal.h
+++ b/shared/nm-utils/nm-macros-internal.h
@@ -45,6 +45,18 @@
 #define nm_auto(fcn)         __attribute__ ((__cleanup__(fcn)))
 
 
+/* This is required to make LTO working.
+ *
+ * See https://gitlab.freedesktop.org/NetworkManager/NetworkManager/merge_requests/76#note_112694
+ *     https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48200#c28
+ */
+#ifndef __clang__
+#define _nm_externally_visible __attribute__ ((__externally_visible__))
+#else
+#define _nm_externally_visible
+#endif
+
+
 #if __GNUC__ >= 7
 #define _nm_fallthrough      __attribute__ ((__fallthrough__))
 #else
@@ -1289,7 +1301,7 @@ fcn_name (lookup_type val) \
 
 #define _NM_BACKPORT_SYMBOL_IMPL(version, return_type, orig_func, versioned_func, args_typed, args) \
 return_type versioned_func args_typed; \
-__attribute__ ((externally_visible)) return_type versioned_func args_typed \
+_nm_externally_visible return_type versioned_func args_typed \
 { \
     return orig_func args; \
 } \