Remove the LINK_LANGUAGE generator expression.

It accepted an optional argument to test for equality, but no way
to get the linker language of a particular target.

TARGET_PROPERTY provides this flexibility and STREQUAL provides
the necessary API for equality test.

Extend the CompileDefinitions test to cover accessing the
property of another target.
Genex: Fix $<CONFIG> with IMPORTED targets and multiple locations.

The old code checked only that there was a LOCATION for the
specified config, but did not check whether the config actually
mapped.

Task-number: 14292
Merge branch 'fix-mapped-config-genex' into remove-LINK_LANGUAGE-genex
Merge topic 'remove-LINK_LANGUAGE-genex' into next

c6734ef Merge branch 'fix-mapped-config-genex' into remove-LINK_LANGUAGE-genex
10a069b Genex: Fix $<CONFIG> with IMPORTED targets and multiple locations.
4f6bd70 Remove the LINK_LANGUAGE generator expression.