gc.c: tick for POWER arch

* gc.c (tick): Use __builtin_ppc_get_timebase for POWER arch.
  [Fix GH-1291]

This gives a little performance improvement

        user     system      total        real
Before: 20.870000   0.000000  20.870000 ( 20.893959)
After:  20.720000   0.000000  20.720000 ( 20.733970)

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54145 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Thu Mar 17 17:14:51 2016  Dinar Valeev  <dvaleev@suse.com>
+
+	* gc.c (tick): Use __builtin_ppc_get_timebase for POWER arch.
+	  [Fix GH-1291]
+
 Thu Mar 17 11:51:48 2016  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* lib/securerandom.rb (gen_random): to avoid blocking on Windows.

gc.c

@@ -935,6 +935,18 @@ tick(void)
     return ((unsigned long long)lo)|( ((unsigned long long)hi)<<32);
 }
 
+#elif defined(__powerpc64__) && \
+	( __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 8)
+typedef unsigned long long tick_t;
+#define PRItick "llu"
+
+static __inline__ tick_t
+tick(void)
+{
+    unsigned long long val = __builtin_ppc_get_timebase();
+    return val;
+}
+
 #elif defined(_WIN32) && defined(_MSC_VER)
 #include <intrin.h>
 typedef unsigned __int64 tick_t;