flac: fix build issues with e500v2 (gnuspe) toolchain
For a PPC target flac will try to build with altivec optimizations.
Altivec and SPE are mutually exclusive options. Between flac's
configure choices and the ppce500v2 tune file options we'd end up with
a compile invocation with the following arguments:
-mabi=spe -mspe -mabi=altivec -maltivec
Which would cause the compile to fail due to the mutual exclusion.
Pulled in a patch from the debian SPE port that addresses this issue:
