Fix for RT#2353: catch yyparse() exceptions in (?{...})

Fix for RT#2353: catch yyparse() exceptions in (?{...})

Ticket is entitled:
"panic: top_env when localizing a lexical variable in qr{(?{...})}"

but a better description would be:
"(?{...}) does not catch yyparse() exceptions in regex compilation"

Changes Perl_sv_compile_2op() to tell doeval() that it must use
S_try_yyparse() to catch any exception that yyparse() may throw.