Update the platform module added by commit 462fbd1e (Add support for
ARTOS platform using GNU C with ac compiler driver, 2015-08-13,
v3.4.0-rc1~201^2) to tell `find_library` to consider library file names
starting in `lib`.

FindEXPAT needs this on ARTOS since commit 13079f38 (FindEXPAT: Fix
for debug and other modified builds, 2023-02-18, v3.27.0-rc1~463^2)
removed its explicit `libexpat` library name candidate.

Fixes: #25776