enable_language: Clarify documentation

Describe explicitly the scope in which enable_language must be
invoked to handle all direct and indirect uses of a language.

While at it, re-word documentation of the OPTIONAL keyword to
avoid confusion over its partial implementation.
Merge topic 'doc-enable_language-scope' into next

b3b57e7 enable_language: Clarify documentation
cmCryptoHash: Increase alignment of HashFile buffer

The SHA512_Update implementation accesses input data via 64-bit
integers.  This requires alignment of the input buffer on some
architectures.  Align our stack-allocated buffer for file content to
satisfy this requirement.
Merge topic 'sha2-alignment' into next

75994d9 cmCryptoHash: Increase alignment of HashFile buffer