Move #includes out of extern "C" blocks

Do some include shuffling for `**.h` files within lib, programs, tests, and zlibWrapper.
`lib/legacy` and `lib/deprecated` are untouched.
`#include`s within `extern "C"` blocks in .cpp files are untouched.

todo: shuffling for `xxhash.h`

lib/zstd.h

@@ -7,16 +7,22 @@
  * in the COPYING file in the root directory of this source tree).
  * You may select, at your option, one of the above-listed licenses.
  */
-#if defined (__cplusplus)
-extern "C" {
-#endif
 
 #ifndef ZSTD_H_235446
 #define ZSTD_H_235446
 
+
 /* ======   Dependencies   ======*/
 #include <stddef.h>   /* size_t */
 
+#include "zstd_errors.h" /* list of errors */
+#if defined(ZSTD_STATIC_LINKING_ONLY) && !defined(ZSTD_H_ZSTD_STATIC_LINKING_ONLY)
+#include <limits.h>   /* INT_MAX */
+#endif /* ZSTD_STATIC_LINKING_ONLY */
+
+#if defined (__cplusplus)
+extern "C" {
+#endif
 
 /* =====   ZSTDLIB_API : control library symbols visibility   ===== */
 #ifndef ZSTDLIB_VISIBLE
@@ -240,7 +246,6 @@ ZSTDLIB_API size_t ZSTD_compressBound(size_t srcSize); /*!< maximum compressed s
 
 
 /*======  Error helper functions  ======*/
-#include "zstd_errors.h" /* list of errors */
 /* ZSTD_isError() :
  * Most ZSTD_* functions returning a size_t value can be tested for error,
  * using ZSTD_isError().
@@ -1215,8 +1220,6 @@ ZSTDLIB_API size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict);
 #if defined(ZSTD_STATIC_LINKING_ONLY) && !defined(ZSTD_H_ZSTD_STATIC_LINKING_ONLY)
 #define ZSTD_H_ZSTD_STATIC_LINKING_ONLY
 
-#include <limits.h>   /* INT_MAX */
-
 /* This can be overridden externally to hide static symbols. */
 #ifndef ZSTDLIB_STATIC_API
 #  if defined(ZSTD_DLL_EXPORT) && (ZSTD_DLL_EXPORT==1)