[test][sanitizer] Temporarily disable test

Test, as expected, fails with Asan on system with 5lvl page tables.
Disabling the test to migrate buildbot.

Author: vitalybuka

compiler-rt/test/sanitizer_common/TestCases/Linux/mmap_56bit_test.c

@@ -1,6 +1,9 @@
 // RUN: %clang %s -pie -fPIE -o %t && %run %t
 // REQUIRES: x86_64-target-arch
 
+// FIXME: Fails Asan, as expected, with 5lvl page tables.
+// UNSUPPORTED: x86_64-target-arch
+
 #include <assert.h>
 #include <stdio.h>
 #include <sys/mman.h>