android: Make a $(PKG_CONFIG) helper variable

This will reduce the amount of copy&paste in the rules.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
android: Drop libtomcrypt dependency

Now that stoken-0.81 can link against nettle, we don't need to build
tomcrypt.

Unfortunately the icky "missing Libs.private" hack from commit
0e6f0ad3a51d7 ("Android: Build GnuTLS from git") now needs to be applied
for libstoken as well, to avoid undefined symbols.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
android: Build openconnect binary as PIE

For 32-bit hosts, the ABI has been slowly changing over the past ~3 years:

 - <= ICS 4.0: Only non-PIE binaries are supported
 - JB 4.1 .. KK 4.4: Both PIE and non-PIE binaries are supported
 - >= L 5.0: Only PIE binaries are supported

So, we need to build a PIE executable in order for it to run at all on
>= 5.0.  Also, PIE will be mandatory on the new 64-bit devices.

See also:
https://code.google.com/p/android-developer-preview/issues/detail?id=888

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
android: Import run_pie helper program from Chromium

This allows the position-independent openconnect binary to run on
ICS (4.0) devices.  /system/bin/linker on ICS does not natively support
PIE.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
android: Fix bogus liboath pathname

There is no $(OATH_BUILD)/liboath.la, so the target will get re-run on
every make invocation.  Correct the path so that make skips the completed
OATH dependency.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>