Add clock counter for hppa architecture

Add support for time measurements on hppa, otherwise build breaks with this
compiler error:
 You need to define CycleTimer for your OS and CPU

Author: Helge Deller

third-party/benchmark/src/cycleclock.h

@@ -228,6 +228,16 @@ inline BENCHMARK_ALWAYS_INLINE int64_t Now() {
   struct timeval tv;
   gettimeofday(&tv, nullptr);
   return static_cast<int64_t>(tv.tv_sec) * 1000000 + tv.tv_usec;
+#elif defined(__hppa__)
+  // HP PA-RISC provides a user-readable clock counter (cr16), but
+  // it's not syncronized across CPUs and only 32-bit wide when programs
+  // are built as 32-bit binaries.
+  // Use clock_gettime(CLOCK_MONOTONIC, ...) instead of gettimeofday
+  // because is provides nanosecond resolution.
+  // Initialize to always return 0 if clock_gettime fails.
+  struct timespec ts = {0, 0};
+  clock_gettime(CLOCK_MONOTONIC, &ts);
+  return static_cast<int64_t>(ts.tv_sec) * 1000000000 + ts.tv_nsec;
 #else
   // The soft failover to a generic implementation is automatic only for ARM.
   // For other platforms the developer is expected to make an attempt to create