volk: clang sets GNUC_MINOR only to 2, so we need to check if we're building with clang. This patch enables xgetbv for clang >= 3.0.
volk: some versions of clang have problems with cvtpi32_ps.

We make a separate cmake check here for xgetbv and cvtpi32_ps and set definitions accordingly.
volk: test for clang version; if less than 3.2, disable SSE4a machine due to a bug in the compiler support.
filter: fixed an issue with filter delays for interp and rational_resampler filters.
grc: fix variable vlen for grc generated hier blocks
analog: additional docs for noise sources.
cmake: If Ice 3.4 found, check version of GCC and disable if >= 4.7.
volk: modifying tests for AVX and SSE4a support in compiler/CPU.
Merge remote-tracking branch 'skoslowski/grc_vlen_hier_fix' into maint