Merge pull request #4218 from facebook/externC

Move #includes out of `extern "C"` blocks

lib/common/zstd_trace.h

@@ -11,10 +11,6 @@
 #ifndef ZSTD_TRACE_H
 #define ZSTD_TRACE_H
 
-#if defined (__cplusplus)
-extern "C" {
-#endif
-
 #include <stddef.h>
 
 /* weak symbol support
@@ -157,8 +153,4 @@ ZSTD_WEAK_ATTR void ZSTD_trace_decompress_end(
 
 #endif /* ZSTD_TRACE */
 
-#if defined (__cplusplus)
-}
-#endif
-
 #endif /* ZSTD_TRACE_H */