Make it possible to set profiles per product.

Use case 1: Build product A for architecture X and product B
for architecture Y (e.g. host tools vs target libraries).
Use case 2: Build product A for architectures X and Y and
product B only for architecture X (e.g. Android
multi-arch packages).

Change-Id: I2eb721c37cdd12c298ee12bad60e21e94b04676b
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>