Qt Creator passes -DANDROID_NDK to the main project configuration
whereas the Qt toolchain file expects -DANDROID_NDK_ROOT.
This causes the configuration of the sub-builds to fail not finding
the android toolchain, and trying to use the CI ndk toolchain path.
Make sure to consider both variables.
Also change the conditions to evaluate the variable as a variable
explicitly, to avoid passing an empty option if the variable is
unset. If the variable is unset, CMake would treat the variable as
an actual string which would always not equal the empty string.
Amends d6919b073a
Pick-to: 6.3 6.4
Task-number: QTBUG-104013
Task-number: QTBUG-102041
Change-Id: Ifee48953ce50bc616c49c59d72e845c6d9418187
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>
5ddb13d0d4