[Patch-gnuradio] Add possibility to disable NEON optimisation on ARM

[Jaroslav Skarvada]

Hi,

the NEON optimisation is always used on all ARMs, even if not
supported. Another problem is that in Fedora we build with
-march=armv7-a -mfpu=vfpv3-d16 -mfloat-abi=hard, so
the compilation fails even on machine with NEON.

The proposed patch adds guard to NEON assembly code and the guard
depends on have_mfpu_neon cmake internal variable. The value of
this variable is autodetected during cmake initialisation, but
can be also overriden by e.g.:

cmake -Dhave_mfpu_neon=0

The performance/usability of binary compiled without NEON is
probably not good, but at least it compiles fine on more
machines.

This issue was originally reported in:
https://bugzilla.redhat.com/show_bug.cgi?id=837028

regards

Jaroslav

gnuradio-3.6.1-neon.patch
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