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/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