As it might be dangerous to use it.
This introduces `LTC_FAST_TYPE_{ASSIGN,MASK,XOR{2,3}}()` in order to
replace the potential unaligned loads.
This fixes the following UBSAN errors:
src/modes/ctr/ctr_encrypt.c:56:66: runtime error: load of misaligned address 0x7ffea07ee82f for type 'LTC_FAST_TYPE', which requires 8 byte alignment
src/modes/ctr/ctr_encrypt.c:56:64: runtime error: store to misaligned address 0x7ffea07ee82f for type 'LTC_FAST_TYPE', which requires 8 byte alignment
tests/store_test.c:66:91: runtime error: load of misaligned address 0x7ffdd32f0d9f for type 'LTC_FAST_TYPE', which requires 8 byte alignment
tests/store_test.c:66:52: runtime error: load of misaligned address 0x7ffdd32f0d71 for type 'LTC_FAST_TYPE', which requires 8 byte alignment
tests/store_test.c:66:50: runtime error: store to misaligned address 0x7ffdd32f0dc1 for type 'LTC_FAST_TYPE', which requires 8 byte alignment
src/mac/pmac/pmac_process.c:40:50: runtime error: load of misaligned address 0x57c89c4329ec for type 'LTC_FAST_TYPE', which requires 8 byte alignment
src/mac/xcbc/xcbc_process.c:35:60: runtime error: load of misaligned address 0x57c89c432ccc for type 'LTC_FAST_TYPE', which requires 8 byte alignment
src/mac/f9/f9_process.c:39:58: runtime error: load of misaligned address 0x5c2b1a1d2c14 for type 'LTC_FAST_TYPE', which requires 8 byte alignment
src/encauth/gcm/gcm_process.c:82:58: runtime error: load of misaligned address 0x596b3e6aa354 for type 'LTC_FAST_TYPE', which requires 8 byte alignment
src/encauth/siv/siv.c:164:19: runtime error: null pointer passed as argument 2, which is declared to never be null
/usr/include/string.h:44:28: note: nonnull attribute specified here
src/misc/compare_testvector.c:63:25: runtime error: null pointer passed as argument 2, which is declared to never be null
/usr/include/string.h:65:33: note: nonnull attribute specified here
