This fixes:

- Undefined function pointer casts.
- Missing X509_INFO_new malloc failure checks.
- Pointless (int) cast on strlen.
- Missing ERR_GET_LIB in PEM_R_NO_START_LINE check.
- Broken error-handling if passing in an existing stack and we hit a
  syntax error.

Bug: chromium:785442
Change-Id: I8be3523b0f13bdb3745938af9740d491486f8bf1
Reviewed-on: https://boringssl-review.googlesource.com/32109
Reviewed-by: Adam Langley <agl@google.com>