Revert fixes to allocation of regex matching

Revert fixes to allocation of regex matching

The fix was not complete, and completing it was proving too complicated.

- Revert "* src/regex.c (re_search_2): Make new code safe for
          -Wjump-misses-init."
  This reverts commit c2a17924a57483d14692c8913edbe8ad24b5ffbb.
- Revert "Port to GCC 6.2.1 + --enable-gcc-warnings"
  This reverts commit f6134bbda259c115c06d4a9a3ab5c39340a15949.
- Revert "Fix handling of allocation in regex matching"
  This reverts commit ad66b3fadb7ae22a4cbb82bb1507c39ceadf3897.
- Revert "Fix handling of buffer relocation in regex.c functions"
  This reverts commit ee04aedc723b035eedaf975422d4eb242894121b.