Use fallthrough attribute.

Use __attribute__ ((fallthrough)) to indicate switch case fall through
instead of a comment. This ensures that the fallthrough warning is not
triggered even if the file is pre-processed (hence stripping the
comments) before it is compiled.

The actual fallback implementation is hidden behind a FALLBACK macro in
case the compiler doesn't support it.

Finally, the -Wimplict-fallthrough warning was upgraded to only allow
the attribute to satisfy it; a comment alone is no longer sufficient.

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
diff --git a/libdw/ChangeLog b/libdw/ChangeLog
index cb5e61a..7a6d311 100644
--- a/libdw/ChangeLog
+++ b/libdw/ChangeLog
@@ -1,3 +1,8 @@
+2018-02-09  Joshua Watt  <JPEWhacker@gmail.com>
+
+	* cfi.c (execute_cfi): Use FALLTHROUGH macro instead of comment.
+	* dwarf_frame_register.c (dwarf_frame_register): Likewise.
+
 2018-01-22  Mark Wielaard  <mark@klomp.org>
 
 	* Makefile.am (AM_CPPFLAGS): Add -I libdwelf.