In 70360cb11, the ASM variable was moved to the x86-common file
even though the android build file didn't include neither
platform-arch.mk nor platform-x86-common.mk.
Instead of explicitly declaring ASM here, include platform-arch.mk
and remove setting of the flags that platform-arch.mk sets.
This is inspired by and based on a patch by Licai Guo.
This will make the normal C++ code not run on non-NEON devices at
all, making the runtime CPU feature detection pointless.
Adding -mfpu=neon to CFLAGS is not necessary, it's enough to
add it while building those individual .S files (via ASMFLAGS).
The USE_ASM variable is architecture independent now and only
controls whether assembly optimizations should be enabled in
the general sense, regardless of the target architecture.
This allows building (and running) codec_unittest for android.
This explicitly needs to go at the end of the LDFLAGS, since both
this and -lgtest etc. are static libraries, and code in gtest
relies on the STL. Since this explicitly needs to be at the end,
a separate makefile variable is added for it.
The main purpose is to make sure that the build doesn't fail
if the build directory contains the gtest subdirectory, although
the unittests also could be run on a device.
One doesn't need to run the ndk-build command from within the
jni subdirectory, calling it from the project top level directory
works just as well.
Also remove an unnecessary step of cd ../../../.. at the end -
since all make commands are run in a subshell, we don't need to
restore the current working directory afterwards.
