Add x86 64bit asm code for downsample
Ignore files produced by the new binary comparison tool
    interface update
Avoid repeated code for getting the android toolchain prefix
Only build the needed binaries in run_PrepareAllTestData.sh

Previously this did a full make, including all of gtest and the unit
test suite. This was done before every build, even for the binary
comparison tests which doesn't use the unit test.

This reduces the runtime of run_PrepareAllTestData.sh from 52 to 10
seconds in one setup.
Use $(OutDir) instead of hardcoding the directory name

This is how it is done in the other projects.
Set optimizer options in WelsVP similarly to the other encoder projects
Remove stray optimization options from the WelsEncPlus project

There's not much performance critical code within this lib, all
the performance critical code in the encoder is in WelsEncCore and
WelsVP, so there's little point in having an extra odd option enabled
here.
speed up memory loading in arm64 MC
Set -Zi instead of -ZI when building with MSVC in debug mode

The -ZI option is only supported when building for 32 bit x86,
when building for x64 or for arm, it gives the warning "/ZI is
not supported on this platform; enabling /Zi instead".

-ZI is for "edit & continue" debugging, which one probably wouldn't
be doing with a build outside of the IDE anyway, so keep it simple
instead of trying to set -ZI specifically for x86 32 bit builds.
Pull gmp-api by branch name
Merge pull request #1128 from mstorsjo/reduce-prepare-compilation

Only build the needed binaries in run_PrepareAllTestData.sh
Merge pull request #1119 from mstorsjo/update-gitignore

Ignore files produced by the new binary comparison tool
Merge pull request #1135 from mstorsjo/msvc-make-debug-option

Set -Zi instead of -ZI when building with MSVC in debug mode
Merge pull request #1133 from dongzha/SpeedupArm64Neon

speed up memory loading in arm64 MC
Merge pull request #1131 from mstorsjo/avoid-hardcoding-paths

Use $(OutDir) instead of hardcoding the directory name
Merge pull request #1126 from mstorsjo/android-simplify

Avoid repeated code for getting the android toolchain prefix
Merge pull request #1137 from ethanhugg/gmpapi-bybranch32

Pull gmp-api by branch name
Align C version to asm function.
Merge pull request #1121 from ruil2/interface_update_1

    interface update