Fix cwrapper argument mangling on w32.

Fix cwrapper argument mangling on w32.

* libltdl/config/ltmain.m4sh (func_emit_cwrapperexe_src): On
mingw, preprocess the argument vector through prepare_spawn.
* tests/execute-mode.at (execute mode): Output args
newline-separated.  Extend tests by more argument pairs that
contain special characters, where the w32 cwrapper fails.
Also test a real compiled program, linked against an uninstalled
library, to expose cwrapper issues.
* NEWS: Update.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>