Compilation fixes for powerpc build, -Wparentheses-equality error and missing header guards

Summary:
This pull request contains miscellaneous compilation fixes.

Thanks,
Chinmay
Closes https://github.com/facebook/rocksdb/pull/3462

Differential Revision: D6941424

Pulled By: sagar0

fbshipit-source-id: fe9c26507bf131221f2466740204bff40a15614a

monitoring/perf_context_imp.h

@@ -43,7 +43,7 @@ extern __thread PerfContext perf_context;
 
 #define PERF_CONDITIONAL_TIMER_FOR_MUTEX_GUARD(metric, condition)       \
   PerfStepTimer perf_step_timer_##metric(&(perf_context.metric), true); \
-  if ((condition)) {                                                    \
+  if (condition) {                                                      \
     perf_step_timer_##metric.Start();                                   \
   }
 

tools/db_stress.cc

@@ -28,7 +28,10 @@ int main() {
 }
 #else
 
+#ifndef __STDC_FORMAT_MACROS
 #define __STDC_FORMAT_MACROS
+#endif  // __STDC_FORMAT_MACROS
+
 #include <fcntl.h>
 #include <inttypes.h>
 #include <stdio.h>

tools/write_stress.cc

@@ -56,7 +56,10 @@ int main() {
 }
 #else
 
+#ifndef __STDC_FORMAT_MACROS
 #define __STDC_FORMAT_MACROS
+#endif // __STDC_FORMAT_MACROS
+
 #include <inttypes.h>
 #include <atomic>
 #include <random>

util/crc32c.cc

@@ -39,8 +39,10 @@
 namespace rocksdb {
 namespace crc32c {
 
+#if defined(HAVE_POWER8) && defined(HAS_ALTIVEC)
 #ifdef __powerpc64__
 static int arch_ppc_crc32 = 0;
+#endif /* __powerpc64__ */
 #endif
 
 static const uint32_t table0_[256] = {