Replace unmangle with cygpath (#1490)

Use `-m` not `-w` so paths use forward slashes

test/CMakeLists.txt

@@ -2,18 +2,12 @@
 
 add_executable(randtilegen gfx/randtilegen.cpp)
 add_executable(rgbgfx_test gfx/rgbgfx_test.cpp)
-add_executable(unmangle link/unmangle.cpp)
 
 install(TARGETS randtilegen rgbgfx_test
         DESTINATION ${rgbds_SOURCE_DIR}/test/gfx
         COMPONENT "Test support programs"
         EXCLUDE_FROM_ALL
         )
-install(TARGETS unmangle
-        DESTINATION ${rgbds_SOURCE_DIR}/test/link
-        COMPONENT "Test support programs"
-        EXCLUDE_FROM_ALL
-        )
 
 foreach(TARGET randtilegen rgbgfx_test)
   if(LIBPNG_FOUND) # pkg-config