dct/rdft: Add missing typedefs for context structs

Without the typedefs there can be trouble depending on #include order.
fft-test: Drop unnecessary #ifdefs around header includes
fft-test: Comment some #endifs
configure: Extend the neon intrinsics check

Check for an instruction that causes the (very old) Apple GCC 4.2
to error out ("unrecognizable insn").

Signed-off-by: Martin Storsjö <martin@martin.st>
Merge commit '11c7155cce50971a38e6cebd39a3ba5a54645fae'

* commit '11c7155cce50971a38e6cebd39a3ba5a54645fae':
  dct/rdft: Add missing typedefs for context structs

Not merged, as it breaks build

Merged-by: Michael Niedermayer <michaelni@gmx.at>
avcodec: dct/rdft only support float mode, skip their contents for fixed point
Merge commit '57f1b1dcc77a93c2a5c503d4e47fe2f567cf9db5'

* commit '57f1b1dcc77a93c2a5c503d4e47fe2f567cf9db5':
  fft-test: Drop unnecessary #ifdefs around header includes

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '5be7d8597d02bcaba2de2503c0e59cf865c746dc'

* commit '5be7d8597d02bcaba2de2503c0e59cf865c746dc':
  fft-test: Comment some #endifs

Conflicts:
	libavcodec/fft-test.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '06a1d1323bc8afd03f085ae98d9b74e431b3534e'

* commit '06a1d1323bc8afd03f085ae98d9b74e431b3534e':
  configure: Extend the neon intrinsics check

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Changelog: add "version <next>:" so people dont add new things to the last release

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>