[sanitizer][test] -std=c2x instead of -std=c23

Adjust tests from dd230ef to use
-std=c2x instead, as Clang in release/17.x doesn't support -std=c23.

Author: MaskRay

compiler-rt/test/sanitizer_common/TestCases/scanf.c

@@ -1,6 +1,6 @@
 // RUN: %clang -std=c17 %s -o %t && %run %t
 /// Test __isoc23_* for glibc 2.38+.
-// RUN: %clang -std=c23 %s -o %t && %run %t
+// RUN: %clang -std=c2x %s -o %t && %run %t
 
 #include <assert.h>
 #include <stdarg.h>

compiler-rt/test/sanitizer_common/TestCases/strtol.c

@@ -1,6 +1,6 @@
 // RUN: %clang -std=c17 %s -o %t && %run %t
 /// Test __isoc23_* for glibc 2.38+.
-// RUN: %clang -std=c23 %s -o %t && %run %t
+// RUN: %clang -std=c2x %s -o %t && %run %t
 
 #include <assert.h>
 #include <inttypes.h>