*: don't include standard C headers inside of extern "C"

Including C headers inside of `extern "C"` breaks use from C++. Hoist
the includes of standard C headers above the block so we don't try
to mangle the stdlib.

I initially tried to scope this with a targeted change but it's too
hard to do correctly that way. This way, we avoid whack-a-mole.

Firefox is working around this in their e21461b7b8b39cc31ba53c47d4f6f310c673ff2f
commit.

Bug: https://bugzilla.mozilla.org/1953080

spa/include/spa/control/control.h

@@ -5,13 +5,13 @@
 #ifndef SPA_CONTROL_H
 #define SPA_CONTROL_H
 
+#include <spa/utils/defs.h>
+#include <spa/pod/pod.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#include <spa/utils/defs.h>
-#include <spa/pod/pod.h>
-
 /** \defgroup spa_control Control
  * Control type declarations
  */

spa/include/spa/control/type-info.h

@@ -5,6 +5,10 @@
 #ifndef SPA_CONTROL_TYPES_H
 #define SPA_CONTROL_TYPES_H
 
+#include <spa/utils/defs.h>
+#include <spa/utils/type.h>
+#include <spa/control/control.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -14,10 +18,6 @@ extern "C" {
  * \{
  */
 
-#include <spa/utils/defs.h>
-#include <spa/utils/type.h>
-#include <spa/control/control.h>
-
 /* base for parameter object enumerations */
 #define SPA_TYPE_INFO_Control		SPA_TYPE_INFO_ENUM_BASE "Control"
 #define SPA_TYPE_INFO_CONTROL_BASE		SPA_TYPE_INFO_Control ":"

spa/include/spa/control/ump-utils.h

@@ -6,13 +6,13 @@
 #ifndef SPA_CONTROL_UMP_UTILS_H
 #define SPA_CONTROL_UMP_UTILS_H
 
+#include <errno.h>
+#include <spa/utils/defs.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#include <errno.h>
-#include <spa/utils/defs.h>
-
 #ifndef SPA_API_CONTROL_UMP_UTILS
  #ifdef SPA_API_IMPL
   #define SPA_API_CONTROL_UMP_UTILS SPA_API_IMPL