Upgrade YARA to newer version

[mbandzi]

Decompiler currently uses version based on v3.6.3 release.
New version fixes several bugs in ELF module (#215).

Note: in newer versions, keyword entry_point_for_arch is used instead of old ep_for_arch so Mach-O signatures in support/yara_patterns/tools/macho have to be fixed.

[s3rvac]

What steps are needed to upgrade YARA to its latest version? It would be useful to have a summary so we do not forget something during the upgrade (e.g. regeneration of our static-code signatures in the support package).

[s3rvac]

I am re-opening this issue as we still use YARA 3.6.3 in RetDec (the upgrade to YARA 3.7 is still in an unmerged branch). As both yaracpp and yaramod use YARA 3.8, we should also use YARA 3.8 in RetDec.