We test this by adding export(TARGETS) to the LinkLanguage test to
export the executable before the library is linked to it. Since
export(TARGETS) computes the link interface of the target (so that it
can export it), this ensures that the information is recomputed after
the link library is added.
This test creates a C executable that links to a C++ static library. On
most platforms the executable will not link unless the C++ linker is
chosen correctly.