fftw3 neon support ICEs

fftw3 (FFT library) has SIMD support for various architectures. This was naively enabled in 3.3.3-6 debian package in a way that didn't work. https://bugs.launchpad.net/linaro-aarch64/+bug/1267107 provides a patche that configures this to build.
All the code is C so has a fighting chance of working on armv8, but unfortunately it reveals an ICE.

Note that full support in this library would inclcude double (and maybe quad?) precision code for neon. Currently only the single-precision build is done.

This was tested with the debian ftw3-3.3.3-7 package.

cd dft/simd/neon
/bin/bash ../../../libtool --tag=CC --mode=compile gcc -std=gnu99 -DHAVE_CONF
IG_H -I. -I../../.. -I../../../kernel -I../../../dft -I../../../dft/simd -I../../../simd-support -D_FORTIFY_SOURCE=2 -g -O2 -Wformat -Werror=format
-security -O2 -MT n1fv_15.lo -MD -MP -MF .deps/n1fv_15.Tpo -c -o n1fv_15.lo n1fv_15.c

Libtool hides the failure result, but it is revealed with:
gcc -std=gnu99 -DHAVE_CONFIG_H -I. -I../../.. -I../../../kernel -I../../../dft -
I../../../dft/simd -I../../../simd-support -D_FORTIFY_SOURCE=2 -g -O2 -Wformat -Werror=format-security -O2 -MT n1fv_15.lo -MD -MP -MF .deps/n1fv_15.T
po -c n1fv_15.c -o n1fv_15.o
In file included from n1fv_15.c:3:0:
../common/n1fv_15.c: In function 'n1fv_15':
../common/n1fv_15.c:337:1: internal compiler error: in simplify_const_unary_operation, at simplify-rtx.c:1503
 }
 ^

Attached is the pre-processed source output from the above failure.