This patch makes the POWER7 optimized strcspn generic by using
default doubleword stores to zero the hash, instead of VSX
instructions. Performance on POWER7/POWER8 does not change.
This patch add a optimized strcspn for POWER7 by using a different
algorithm than default implementation: it constructs a table based on
the 'accept' argument and use this table to check for any occurance
on the input string. The idea is similar as x86_64 uses.
For PowerPC some tunings were added, such as unroll loops and align
stack memory to table to 16 bytes (so VSX clean can ran without
alignment issues).
