add_custom_command: Support generator expressions for DEPENDS

Evaluate the depends for all configurations and depend on the union
of resulting files.
Qt4: Fix moc command dependencies for incremental build.

Since commit v2.8.12~327^2 (Qt4Macros: Allow specifying a TARGET
in invokations of macros., 2013-02-26), a parameters file is
populated with moc arguments at generate-time.

When the compile definitions or include directories change, the
parameters file is updated but moc is not re-run in response.

Fix that by making the moc invocation depend on the parameters file.

Reported-At: https://bugreports.qt-project.org/browse/QTBUG-36970
Merge topic 'fix-Qt4-moc-command-depends' into next

db8382d8 Qt4: Fix moc command dependencies for incremental build.
599c059a add_custom_command: Support generator expressions for DEPENDS
Fix typo.
Merge topic 'fix-Qt4-moc-command-depends' into next

1e6ef747 Fix typo.