[arm64] Negative immediates and lack of default Neon support

[Torbjörn Granlund]

Marc Glisse <marc.glisse at inria.fr> writes:

  Can't we compile something that will fail without neon and add
  -mfpu=neon only in that case? Otherwise, the warning is bearable.
  
We get many lines of warnings about unused -I and -D already from clang.
Those are the silliest warnings, and also hard to suppress (except in
clang).

clang: warning: argument unused during compilation: '-D HAVE_CONFIG_H'
clang: warning: argument unused during compilation: '-I .'
clang: warning: argument unused during compilation: '-I gmp/mpn'
clang: warning: argument unused during compilation: '-I ..'
clang: warning: argument unused during compilation: '-D __GMP_WITHIN_GMP'
clang: warning: argument unused during compilation: '-I gmp'
clang: warning: argument unused during compilation: '-D OPERATION_add_n'

Perhaps one could pass some command line option to clang to avoid some
of the strangest warnings?

-- 
Torbjörn
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