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/common/bitstream.h

@@ -14,9 +14,6 @@
 #ifndef BITSTREAM_H_MODULE
 #define BITSTREAM_H_MODULE
 
-#if defined (__cplusplus)
-extern "C" {
-#endif
 /*
 *  This API consists of small unitary functions, which must be inlined for best performance.
 *  Since link-time-optimization is not available for all compilers,
@@ -32,7 +29,6 @@ extern "C" {
 #include "error_private.h"  /* error codes and messages */
 #include "bits.h"           /* ZSTD_highbit32 */
 
-
 /*=========================================
 *  Target specific
 =========================================*/
@@ -44,6 +40,10 @@ extern "C" {
 #  endif
 #endif
 
+#if defined (__cplusplus)
+extern "C" {
+#endif
+
 #define STREAM_ACCUMULATOR_MIN_32  25
 #define STREAM_ACCUMULATOR_MIN_64  57
 #define STREAM_ACCUMULATOR_MIN    ((U32)(MEM_32bits() ? STREAM_ACCUMULATOR_MIN_32 : STREAM_ACCUMULATOR_MIN_64))

lib/common/debug.h

@@ -32,10 +32,6 @@
 #ifndef DEBUG_H_12987983217
 #define DEBUG_H_12987983217
 
-#if defined (__cplusplus)
-extern "C" {
-#endif
-
 
 /* static assert is triggered at compile time, leaving no runtime artefact.
  * static assert only works with compile-time constants.
@@ -75,9 +71,12 @@ extern "C" {
 #  endif
 #endif
 
+#if defined (__cplusplus)
+extern "C" {
+#endif
+
 #if (DEBUGLEVEL>=2)
 #  define ZSTD_DEPS_NEED_IO
-#  include "zstd_deps.h"
 extern int g_debuglevel; /* the variable is only declared,
                             it actually lives in debug.c,
                             and is shared by the whole process.

lib/common/error_private.h

@@ -13,11 +13,6 @@
 #ifndef ERROR_H_MODULE
 #define ERROR_H_MODULE
 
-#if defined (__cplusplus)
-extern "C" {
-#endif
-
-
 /* ****************************************
 *  Dependencies
 ******************************************/
@@ -26,6 +21,9 @@ extern "C" {
 #include "debug.h"
 #include "zstd_deps.h"       /* size_t */
 
+#if defined (__cplusplus)
+extern "C" {
+#endif
 
 /* ****************************************
 *  Compiler-specific

lib/common/fse.h

@@ -11,11 +11,6 @@
  * 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 FSE_H
 #define FSE_H
 
@@ -25,6 +20,14 @@ extern "C" {
 ******************************************/
 #include "zstd_deps.h"    /* size_t, ptrdiff_t */
 
+#if defined(FSE_STATIC_LINKING_ONLY) && !defined(FSE_H_FSE_STATIC_LINKING_ONLY)
+#define FSE_H_FSE_STATIC_LINKING_ONLY
+#include "bitstream.h"
+#endif 
+
+#if defined (__cplusplus)
+extern "C" {
+#endif
 
 /*-*****************************************
 *  FSE_PUBLIC_API : control library symbols visibility
@@ -233,9 +236,6 @@ If there is an error, the function will return an error code, which can be teste
 #if defined(FSE_STATIC_LINKING_ONLY) && !defined(FSE_H_FSE_STATIC_LINKING_ONLY)
 #define FSE_H_FSE_STATIC_LINKING_ONLY
 
-/* *** Dependency *** */
-#include "bitstream.h"
-
 
 /* *****************************************
 *  Static allocation

lib/common/huf.h

@@ -12,10 +12,6 @@
  * You may select, at your option, one of the above-listed licenses.
 ****************************************************************** */
 
-#if defined (__cplusplus)
-extern "C" {
-#endif
-
 #ifndef HUF_H_298734234
 #define HUF_H_298734234
 
@@ -25,6 +21,9 @@ extern "C" {
 #define FSE_STATIC_LINKING_ONLY
 #include "fse.h"
 
+#if defined (__cplusplus)
+extern "C" {
+#endif
 
 /* ***   Tool functions *** */
 #define HUF_BLOCKSIZE_MAX (128 * 1024)   /**< maximum input size for a single block compressed with HUF_compress */

lib/common/mem.h

@@ -11,10 +11,6 @@
 #ifndef MEM_H_MODULE
 #define MEM_H_MODULE
 
-#if defined (__cplusplus)
-extern "C" {
-#endif
-
 /*-****************************************
 *  Dependencies
 ******************************************/
@@ -77,6 +73,10 @@ extern "C" {
 #endif
 
 
+#if defined (__cplusplus)
+extern "C" {
+#endif
+
 /*-**************************************************************
 *  Memory I/O API
 *****************************************************************/

lib/common/pool.h

@@ -11,15 +11,15 @@
 #ifndef POOL_H
 #define POOL_H
 
-#if defined (__cplusplus)
-extern "C" {
-#endif
-
 
 #include "zstd_deps.h"
 #define ZSTD_STATIC_LINKING_ONLY   /* ZSTD_customMem */
 #include "../zstd.h"
 
+#if defined (__cplusplus)
+extern "C" {
+#endif
+
 typedef struct POOL_ctx_s POOL_ctx;
 
 /*! POOL_create() :

lib/common/threading.h

@@ -16,10 +16,6 @@
 
 #include "debug.h"
 
-#if defined (__cplusplus)
-extern "C" {
-#endif
-
 #if defined(ZSTD_MULTITHREAD) && defined(_WIN32)
 
 /**
@@ -60,6 +56,11 @@ extern "C" {
 #define ZSTD_pthread_cond_signal(a)     WakeConditionVariable((a))
 #define ZSTD_pthread_cond_broadcast(a)  WakeAllConditionVariable((a))
 
+
+#if defined (__cplusplus)
+extern "C" {
+#endif
+
 /* ZSTD_pthread_create() and ZSTD_pthread_join() */
 typedef HANDLE ZSTD_pthread_t;
 
@@ -73,10 +74,19 @@ int ZSTD_pthread_join(ZSTD_pthread_t thread);
  */
 
 
+#if defined (__cplusplus)
+}
+#endif
+
 #elif defined(ZSTD_MULTITHREAD)    /* posix assumed ; need a better detection method */
 /* ===   POSIX Systems   === */
 #  include <pthread.h>
 
+
+#if defined (__cplusplus)
+extern "C" {
+#endif
+
 #if DEBUGLEVEL < 1
 
 #define ZSTD_pthread_mutex_t            pthread_mutex_t
@@ -123,9 +133,18 @@ int ZSTD_pthread_cond_destroy(ZSTD_pthread_cond_t* cond);
 
 #endif
 
+#if defined (__cplusplus)
+}
+#endif
+
 #else  /* ZSTD_MULTITHREAD not defined */
 /* No multithreading support */
 
+
+#if defined (__cplusplus)
+extern "C" {
+#endif
+
 typedef int ZSTD_pthread_mutex_t;
 #define ZSTD_pthread_mutex_init(a, b)   ((void)(a), (void)(b), 0)
 #define ZSTD_pthread_mutex_destroy(a)   ((void)(a))

lib/common/zstd_trace.h

@@ -11,12 +11,12 @@
 #ifndef ZSTD_TRACE_H
 #define ZSTD_TRACE_H
 
+#include <stddef.h>
+
 #if defined (__cplusplus)
 extern "C" {
 #endif
 
-#include <stddef.h>
-
 /* weak symbol support
  * For now, enable conservatively:
  * - Only GNUC