Fix OutDir test on HP, MinGW, and Cygwin

The commit "Test per-config OUTPUT_DIRECTORY properties" added this test
with a find_library() call in a CMake script, which requires an explicit
list of possible library prefixes and suffixes.  This commit adds more
suffixes to match the libraries built on HP, MinGW, and Cygwin.

Tests/OutDir/OutDir.cmake

@@ -1,5 +1,5 @@
 set(CMAKE_FIND_LIBRARY_PREFIXES "lib" "")
-set(CMAKE_FIND_LIBRARY_SUFFIXES ".lib" ".a" ".so" ".dylib")
+set(CMAKE_FIND_LIBRARY_SUFFIXES ".lib" ".a" ".so" ".sl" ".dylib" ".dll.a")
 
 find_library(TESTC1_LIB
   NAMES testc1 testc1_test_debug_postfix