selftests/harness: Display signed values correctly

[ Upstream commit d088c92802549fc1cf77a12a4e3986160d63662a ]

Since forever the harness output for signed value tests have reported
unsigned values to avoid casting. Instead, actually test the variable
types and perform the correct casts and choose the correct format
specifiers.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Stable-dep-of: 02bc220dc6dc ("selftests: harness: fix printing of mismatch values in __EXPECT()")
Signed-off-by: Sasha Levin <sashal@kernel.org>