Use LTC_ prefix for all libtomcrypt macros and preprocessor definitions

[mabuchner]

libtomcrypt defines many macros and preprocessor definitions.

Some of them use a LTM_ prefix, but many of them don't.

For example, take a look at the tomcrypt_macros.h.

This can easily cause name collisions.

All macros and preprocessor definitions from libtomcrypt should therefore use a LTC_ prefix.

[mabuchner]

Related to #448.