relationals: fix missing includes (#1753)

With GCC 13 some headers are no longer included transitively through
C++ Standard Library headers.

Signed-off-by: Sven van Haastregt <sven.vanhaastregt@arm.com>

test_conformance/relationals/test_comparisons_fp.cpp

@@ -14,6 +14,8 @@
 // limitations under the License.
 //
 
+#include <cstdint>
+#include <functional>
 #include <iostream>
 #include <map>
 #include <memory>