This will allow per-config destinations for targets in EXPORT sets.
Using multiple install(TARGETS) with separate CONFIGURATIONS is
rejected as a target appearing more than once in an export set.
Now instead one can write
install(TARGETS foo EXPORT exp DESTINATION lib/$<CONFIG>)
to get a single logical membership of the target in the export set
while still having a per-config destination.
We test that LINK_INTERFACE_MULTIPLICITY propagates through export() and
install(EXPORT) into dependent projects. A simple cycle of two archives
that need to be scanned three times ensures that the importing project
uses the multiplicity correctly.
This extends the ExportImport test. The Export project creates a C++
static library and exports it. Then the Import project links the
library into a C executable. On most platforms the executable will link
only if the C++ linker is chosen correctly.
Linking to a Windows shared library (.dll) requires only its import
library (.lib). This teaches CMake to recognize SHARED IMPORTED library
targets that set only IMPORTED_IMPLIB and not IMPORTED_LOCATION.
Brad King