[sanitizer] Assume getrandom might not be supported by the kernel

It was added on kernel 3.17.

compiler-rt/test/sanitizer_common/TestCases/Posix/getrandom.c

@@ -3,6 +3,7 @@
 //
 
 #include <sys/types.h>
+#include <errno.h>
 
 #if !defined(__GLIBC_PREREQ)
 #define __GLIBC_PREREQ(a, b) 0
@@ -21,6 +22,8 @@ int main() {
   ssize_t n = 1;
 #if defined(HAS_GETRANDOM)
   n = getrandom(buf, sizeof(buf), 0);
+  if (n == -1 && errno == ENOSYS)
+    n = 1;
 #endif
   return (int)(n <= 0);
 }