[test][asan] Make the printf-5.c test case actually emit a volatile memcpy.

[pcwalton]

Summary

The current test in printf-5.c appears to try to emit a volatile memcpy for the
format string, but it doesn't because the volatile qualifier is implicitly
casted away. Using a string literal instead preserves the volatile qualifier.

This is a follow-up to D137031 and is a prerequisite for D136822, which elides
memcpys in more instances and would otherwise break this test.

[nikic]

LG

compiler-rt/test/asan/TestCases/printf-5.c

 // RUN: %clang_asan -O2 %s -o %t
 // We need replace_intrin=0 to avoid reporting errors in memcpy.
 // RUN: %env_asan_opts=replace_intrin=0:check_printf=1 not %run %t 2>&1 | FileCheck --check-prefix=CHECK-ON %s
 // RUN: %env_asan_opts=replace_intrin=0:check_printf=0 %run %t 2>&1 | FileCheck --check-prefix=CHECK-OFF %s
 // RUN: %env_asan_opts=replace_intrin=0 not %run %t 2>&1 | FileCheck --check-prefix=CHECK-ON %s
 
 // FIXME: printf is not intercepted on Windows yet.
 // XFAIL: windows-msvc
 
 #include <stdio.h>
 #include <string.h>
 int main() {
   volatile char c = '0';
   volatile int x = 12;
   volatile float f = 1.239;
   volatile char s[] = "34";
-  volatile char fmt[2];
-  memcpy((char *)fmt, "%c %d %f %s\n", sizeof(fmt));
+  volatile char fmt[2] = "%c %d %f %s\n";
   printf((char *)fmt, c, x, f, s);
   return 0;
   // Check that format string is sanitized.
   // CHECK-ON: stack-buffer-overflow
   // CHECK-ON-NOT: 0 12 1.239 34
   // CHECK-OFF: 0
 }