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/compress/zstd_double_fast.h

@@ -11,13 +11,13 @@
 #ifndef ZSTD_DOUBLE_FAST_H
 #define ZSTD_DOUBLE_FAST_H
 
+#include "../common/mem.h"      /* U32 */
+#include "zstd_compress_internal.h"     /* ZSTD_CCtx, size_t */
+
 #if defined (__cplusplus)
 extern "C" {
 #endif
 
-#include "../common/mem.h"      /* U32 */
-#include "zstd_compress_internal.h"     /* ZSTD_CCtx, size_t */
-
 #ifndef ZSTD_EXCLUDE_DFAST_BLOCK_COMPRESSOR
 
 void ZSTD_fillDoubleHashTable(ZSTD_matchState_t* ms,

lib/compress/zstd_fast.h

@@ -11,13 +11,13 @@
 #ifndef ZSTD_FAST_H
 #define ZSTD_FAST_H
 
+#include "../common/mem.h"      /* U32 */
+#include "zstd_compress_internal.h"
+
 #if defined (__cplusplus)
 extern "C" {
 #endif
 
-#include "../common/mem.h"      /* U32 */
-#include "zstd_compress_internal.h"
-
 void ZSTD_fillHashTable(ZSTD_matchState_t* ms,
                         void const* end, ZSTD_dictTableLoadMethod_e dtlm,
                         ZSTD_tableFillPurpose_e tfp);

lib/compress/zstd_lazy.h

@@ -11,12 +11,12 @@
 #ifndef ZSTD_LAZY_H
 #define ZSTD_LAZY_H
 
+#include "zstd_compress_internal.h"
+
 #if defined (__cplusplus)
 extern "C" {
 #endif
 
-#include "zstd_compress_internal.h"
-
 /**
  * Dedicated Dictionary Search Structure bucket log. In the
  * ZSTD_dedicatedDictSearch mode, the hashTable has

lib/compress/zstd_ldm.h

@@ -11,13 +11,13 @@
 #ifndef ZSTD_LDM_H
 #define ZSTD_LDM_H
 
+#include "zstd_compress_internal.h"   /* ldmParams_t, U32 */
+#include "../zstd.h"   /* ZSTD_CCtx, size_t */
+
 #if defined (__cplusplus)
 extern "C" {
 #endif
 
-#include "zstd_compress_internal.h"   /* ldmParams_t, U32 */
-#include "../zstd.h"   /* ZSTD_CCtx, size_t */
-
 /*-*************************************
 *  Long distance matching
 ***************************************/

lib/compress/zstd_opt.h

@@ -11,12 +11,12 @@
 #ifndef ZSTD_OPT_H
 #define ZSTD_OPT_H
 
+#include "zstd_compress_internal.h"
+
 #if defined (__cplusplus)
 extern "C" {
 #endif
 
-#include "zstd_compress_internal.h"
-
 #if !defined(ZSTD_EXCLUDE_BTLAZY2_BLOCK_COMPRESSOR) \
  || !defined(ZSTD_EXCLUDE_BTOPT_BLOCK_COMPRESSOR) \
  || !defined(ZSTD_EXCLUDE_BTULTRA_BLOCK_COMPRESSOR)

lib/compress/zstdmt_compress.h

@@ -11,6 +11,11 @@
  #ifndef ZSTDMT_COMPRESS_H
  #define ZSTDMT_COMPRESS_H
 
+/* ===   Dependencies   === */
+#include "../common/zstd_deps.h"   /* size_t */
+#define ZSTD_STATIC_LINKING_ONLY   /* ZSTD_parameters */
+#include "../zstd.h"            /* ZSTD_inBuffer, ZSTD_outBuffer, ZSTDLIB_API */
+
  #if defined (__cplusplus)
  extern "C" {
  #endif
@@ -25,12 +30,6 @@
  *        otherwise ZSTDMT_createCCtx*() will fail.
  */
 
-/* ===   Dependencies   === */
-#include "../common/zstd_deps.h"   /* size_t */
-#define ZSTD_STATIC_LINKING_ONLY   /* ZSTD_parameters */
-#include "../zstd.h"            /* ZSTD_inBuffer, ZSTD_outBuffer, ZSTDLIB_API */
-
-
 /* ===   Constants   === */
 #ifndef ZSTDMT_NBWORKERS_MAX /* a different value can be selected at compile time */
 #  define ZSTDMT_NBWORKERS_MAX ((sizeof(void*)==4) /*32-bit*/ ? 64 : 256)