mail/exim: update to 4.94.2 security release

• New upstream security release. + Release based on +fixes branch. + Fixes multiple security vulnerabilities reported by Qualys and adds related robustness improvements. (Special thanks to Heiko) CVE-2020-28023: Out-of-bounds read in smtp_setup_msg() CVE-2020-28007: Link attack in Exim's log directory CVE-2020-28016: Heap out-of-bounds write in parse_fix_phrase() CVE-2020-28012: Missing close-on-exec flag for privileged pipe CVE-2020-28024: Heap buffer underflow in smtp_ungetc() CVE-2020-28009: Integer overflow in get_stdinput() CVE-2020-28015, CVE-28021: New-line injection into spool header file CVE-2020-28026: Line truncation and injection in spool_read_header() CVE-2020-28022: Heap out-of-bounds read and write in extract_option() CVE-2020-28017: Integer overflow in receive_add_recipient() CVE-2020-28013: Heap buffer overflow in parse_fix_phrase() CVE-2020-28011: Heap buffer overflow in queue_run() CVE-2020-28010: Heap out-of-bounds write in main() CVE-2020-28018: Use-after-free in tls-openssl.c CVE-2020-28025: Heap out-of-bounds read in pdkim_finish_bodyhash() CVE-2020-28014, CVE-2021-27216: PID file handling CVE-2020-28008: Assorted attacks in Exim's spool directory CVE-2020-28019: Failure to reset function pointer after BDAT error
• Incorporate debian patches to turn taint failures into warnings.

(cherry picked from commit 0a629bd71087f75c3b334edb53b01ec68709ab60)