Use sized integer types rather than unsigned char/int/long. The latter
two are especially a mess as they're both used in lieu of uint32_t.
Sometimes the code just blindly uses unsigned long and sometimes it uses
unsigned int when an LP64 architecture would notice.

Change-Id: I4c5c6aaf82cfe9fe523435588d286726a7c43056
Reviewed-on: https://boringssl-review.googlesource.com/4952
Reviewed-by: Adam Langley <agl@google.com>