[PATCH] cmake: workaround GCC 7.2 segfault on v?sn?printf

[Vladimir Davydov]

On Fri, Dec 28, 2018 at 07:48:54AM +0300, Alexander Turenko wrote:
> GCC 7.2.1 fails like so on our codebase:
> 
> /tarantool/src/lib/json/json.c: In function ‘json_token_snprint’:
> /tarantool/src/lib/json/json.c:324:1: internal compiler error: Segmentation fault
>  json_token_snprint(char *buf, int size, const struct json_token *token,
>  ^~~~~~~~~~~~~~~~~~
> 
> The backtrace of cc1 is the following (failed to install compatible
> debuginfo on Fedora 26, so ??s):
> 
>     #0  0x0000000000d0320c in get_source_location_for_substring(cpp_reader*, string_concat_db*, unsigned int, cpp_ttype, int, int, int, unsigned int*) ()
>     #1  0x00000000005c0e79 in c_get_substring_location(substring_loc const&, unsigned int*) ()
>     #2  0x00000000007f8418 in format_warning_va(substring_loc const&, source_range const*, char const*, int, char const*, __va_list_tag (*) [1]) ()
>     #3  0x00000000007f838b in format_warning_at_substring(substring_loc const&, source_range const*, char const*, int, char const*, ...) ()
>     #4  0x0000000000c72c2d in ?? ()
>     #5  0x0000000000f6f308 in execute_one_pass(opt_pass*) ()
>     #6  0x0000000000787da6 in ?? ()
>     #7  0x00000000012ac338 in symbol_table::compile() ()
>     #8  0x0000000000de650f in symbol_table::finalize_compilation_unit() ()
>     #9  0x00000000012ee8df in ?? ()
>     #10 0x0000000000d3ba84 in toplev::main(int, char**) ()
>     #11 0x0000000000d3d35b in main ()
> 
> The issue in the GCC bugtracker: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83448
> 
> The idea of the commit is to check builtin snprintf with the code from
> GCC test suite and disable all related builtins if the compiler is GCC
> and the case fails.
> 
> We also need to disable FORTIFY_SOURCES in the case, because it uses
> v?sn?printf builtins directly.

Frankly, I don't think it's worth adding a workaround for a buggy
compiler version that's only used by distributions that passed EOL.
IMO we'd better disable compilation for those distributions.