Fix pthread_getcpuclockid.

clock_gettime was returning EINVAL for the values
produced by pthread_getcpuclockid.

Bug: 10346183
Change-Id: Iabe643d7d46110bb311a0367aa0fc737f653208e

libc/bionic/pthread_getcpuclockid.cpp

@@ -36,7 +36,13 @@ int pthread_getcpuclockid(pthread_t t, clockid_t* clockid) {
     return ESRCH;
   }
 
-  enum { CLOCK_IDTYPE_BITS = 3 };
-  *clockid = CLOCK_THREAD_CPUTIME_ID | (thread->tid << CLOCK_IDTYPE_BITS);
+  // The tid is stored in the top bits, but negated.
+  clockid_t result = ~static_cast<clockid_t>(thread->tid) << 3;
+  // Bits 0 and 1: clock type (0 = CPUCLOCK_PROF, 1 = CPUCLOCK_VIRT, 2 = CPUCLOCK_SCHED).
+  result |= 2;
+  // Bit 2: thread (set) or process (clear)?
+  result |= (1 << 2);
+
+  *clockid = result;
   return 0;
 }