src/ : Fix two typos.

* 'norrmal' -> 'normal'.
* 'fames' -> 'frames'.

Reported-by: lvqcl <lvqcl.mail@gmail.com>
Replace FLAC__CPU_X86_64 with FLaC__CPU_X86_64.

Previous autorconf versions had problems with variable begining witj
'FLAC_' (autoconf uses 'AC_').

Reported-by: lvqcl <lvqcl.mail@gmail.com>