Add a test for the interfaces in targets exported from the build tree.
Make the BUILD_INTERFACE of export()ed targets work.

The existing BUILD_INTERFACE code is executed at generate time, which
is too late for export().
Export the INTERFACE_PIC property.
Test evaluation target via export for generator expressions
Merge topic 'test-export-iface-genex' into next

d3a49fb Test evaluation target via export for generator expressions
6172575 Export the INTERFACE_PIC property.
fe45ab0 Make the BUILD_INTERFACE of export()ed targets work.
3a5fb25 Add a test for the interfaces in targets exported from the build tree.