How to cross-compile for Android.

This is known to work at least for Android 3.0 running on a Motorola
Xoom.  Other configurations and toolchains might work, but haven't
been tested.  Feedback is welcome.

You need the android-ndk-r5c native development kit.  Install it
somewhere.  Then do this:

# Maybe not all of these are necessary -- I'm just being cautious.
#
export AR=/path/to/android-ndk-r5c/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-ar
export CPP=/path/to/android-ndk-r5c/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-cpp
export LD=/path/to/android-ndk-r5c/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-ld
export CXX=/path/to/android-ndk-r5c/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-g++
export CC=/path/to/android-ndk-r5c/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-gcc

# Configure.  This will build a Valgrind that needs to go in
# /data/local/Inst on the device and that uses /data/local/tmp
# as the tmp dir on the device.  This means it can operate on
# non-rooted (production) devices.
#

cd trunk
./autogen.sh

CPPFLAGS="--sysroot=/path/to/android-ndk-r5c/platforms/android-3/arch-arm" \
   CFLAGS="--sysroot=/path/to/android-ndk-r5c/platforms/android-3/arch-arm" \
   ./configure --prefix=/data/local/Inst \
   --host=armv7-unknown-linux --target=armv7-unknown-linux \
   --with-tmpdir=/data/local/tmp


# At the end of the configure run, a few lines of details
# are printed.  Make sure that you see these two lines:
#
#          Platform variant: android
#     Primary -DVGPV string: -DVGPV_arm_linux_android=1
#
# If you see anything else at this point, something is wrong, and
# either the build will fail, or will succeed but you'll get something
# which won't work.


# Build, and park the install tree in `pwd`/Inst
make
make install DESTDIR=`pwd`/Inst


# To get the install tree onto the device:
# (I don't know why it's not "adb push Inst /data/local", but this
# formulation does appear to put the result in /data/local/Inst.)
#
adb push Inst /

# To run (on the device)
/data/local/Bin/valgrind [the usual args etc]