configure: add missing x86 dependency for i686
configure: clang: explicitly state dep file and rule name in DEPFLAGS

Fixes dependency file generation with gas-preprocessor.pl and clang.
Flags copied from GCC and tested with Apple's clang from Xcode 5 and
5.1 and clang 3.2, 3.3, 3.4 on Linux.
Merge commit 'fb87e69ff77f96536768dbae01d82db70c8b41f3'

* commit 'fb87e69ff77f96536768dbae01d82db70c8b41f3':
  configure: add missing x86 dependency for i686

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge remote-tracking branch 'qatar/master'

* qatar/master:
  configure: clang: explicitly state dep file and rule name in DEPFLAGS

Merged-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/libfdk_aacenc: enable 7.1 channel encoding

7.1(wide) and 7.1(wide-side) channel layouts are supported in fdk_aac since october 2013 (commit fa3eba1644)

Signed-off-by: Jean First <jeanfirst@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>