build: fixing various warning from clang.

Addresses iss #586; adapted for current set of warnings after patches since this issue was posted.
volk: negate real part of 32fc_s32f_power_32fc to fix results.

Addresses issue #629.
Merge branch 'maint'

Conflicts:
	volk/apps/volk_profile.cc
Merge branch 'master' into next