build netbsd-7 cross-gdb on netbsd-9 host fails due to switch-case fallthrough

["John D. Baker" <jdbaker%consolidated.net@localhost>]

This is the first time building netbsd-7 (sparc) since updating the
build host to netbsd-9 (amd64).  As I build with MKCROSSGDB=yes, it
is failing with:

[...]
/x/netbsd-7/src/tools/gdb/../../external/gpl3/gdb/dist/bfd/coffgen.c: In function 'coff_print_symbol':
/x/netbsd-7/src/tools/gdb/../../external/gpl3/gdb/dist/bfd/coffgen.c:2103:8: error: this statement may fall through [-Werror=implicit-fallthrough=]
     if (combined->u.syment.n_type == T_NULL)
        ^
/x/netbsd-7/src/tools/gdb/../../external/gpl3/gdb/dist/bfd/coffgen.c:2120:3: note: here
   case C_EXT:
   ^~~~
/x/netbsd-7/src/tools/gdb/../../external/gpl3/gdb/dist/bfd/coffgen.c:2122:8: error: this statement may fall through [-Werror=implicit-fallthrough=]
     if (ISFCN (combined->u.syment.n_type))
        ^
/x/netbsd-7/src/tools/gdb/../../external/gpl3/gdb/dist/bfd/coffgen.c:2140:3: note: here
   default:
   ^~~~~~~
[...]
/x/netbsd-7/src/tools/gdb/../../external/gpl3/gdb/dist/bfd/libbfd.h:768:8: error: this statement may fall through [-Werror=implicit-fallthrough=]
   do { bfd_assert(__FILE__,__LINE__); } while (0)
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/x/netbsd-7/src/tools/gdb/../../external/gpl3/gdb/dist/bfd/reloc.c:7256:4: note: in expansion of macro 'BFD_FAIL'
    BFD_FAIL ();
    ^~~~~~~~
mv -f .deps/archive.Tpo .deps/archive.Plo
/x/netbsd-7/src/tools/gdb/../../external/gpl3/gdb/dist/bfd/reloc.c:7257:2: note: here
  case 32:
  ^~~~
[...]
/x/netbsd-7/src/tools/gdb/../../external/gpl3/gdb/dist/bfd/libbfd.h:768:8: error: this statement may fall through [-Werror=implicit-fallthrough=]
   do { bfd_assert(__FILE__,__LINE__); } while (0)
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/x/netbsd-7/src/tools/gdb/../../external/gpl3/gdb/dist/bfd/reloc.c:7260:4: note: in expansion of macro 'BFD_FAIL'
    BFD_FAIL ();
    ^~~~~~~~
/x/netbsd-7/src/tools/gdb/../../external/gpl3/gdb/dist/bfd/reloc.c:7261:2: note: here
  default:
  ^~~~~~~
In file included from /x/netbsd-7/src/tools/gdb/../../external/gpl3/gdb/dist/bfd/reloc.c:52:0:
/x/netbsd-7/src/tools/gdb/../../external/gpl3/gdb/dist/bfd/libbfd.h:768:8: error: this statement may fall through [-Werror=implicit-fallthrough=]
   do { bfd_assert(__FILE__,__LINE__); } while (0)
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/x/netbsd-7/src/tools/gdb/../../external/gpl3/gdb/dist/bfd/reloc.c:7262:4: note: in expansion of macro 'BFD_FAIL'
    BFD_FAIL ();
    ^~~~~~~~
/x/netbsd-7/src/tools/gdb/../../external/gpl3/gdb/dist/bfd/reloc.c:7264:5: note: here
     default:
     ^~~~~~~
[...]


I didn't see this when still using netbsd-8 on the build host.  I suppose
the pedantry came with GCC 7.4.0.  netbsd-8 sources seem to have been
adjusted to cope.  Perhaps netbsd-7 needs similar attention?

Thanks.

-- 
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