dsp.h: collect gcc/clang version test macros

endian_inl.h already relies on dsp.h, grab the definitions from there.

Change-Id: I445f7d0631723043c55da1070498f89965bec7b1
dsp/lossless: workaround gcc-4.9 bug on arm

force Sub3() to not be inlined, otherwise the code in Select() will be
incorrect.
https://android-review.googlesource.com/#/c/102511

Change-Id: I90ae58bf3e6cc92ca9897f69974733d562e29aaf
Speed up Huffman decoding for lossless

speed-up is ~1.6% for photographic image to 10% for graphical image
(1000 images corpus was sped up by 5.8 %)

Code by akramarz@google.com and jyrki@google.com

Change-Id: Iceb2e50e6cc761b9315a3865d22ec9d19b8011c6
address cosmetic comments from patch #71380

Change-Id: Iaba301b9e77aa4febe0efe1e6016fab42d5589f3