*: 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/pod/builder.h

@@ -5,6 +5,12 @@
 #ifndef SPA_POD_BUILDER_H
 #define SPA_POD_BUILDER_H
 
+#include <stdarg.h>
+
+#include <spa/utils/hook.h>
+#include <spa/pod/iter.h>
+#include <spa/pod/vararg.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -18,12 +24,6 @@ extern "C" {
  * \{
  */
 
-#include <stdarg.h>
-
-#include <spa/utils/hook.h>
-#include <spa/pod/iter.h>
-#include <spa/pod/vararg.h>
-
 #ifndef SPA_API_POD_BUILDER
  #ifdef SPA_API_IMPL
   #define SPA_API_POD_BUILDER SPA_API_IMPL

spa/include/spa/pod/command.h

@@ -5,13 +5,13 @@
 #ifndef SPA_COMMAND_H
 #define SPA_COMMAND_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>
-
 /**
  * \addtogroup spa_pod
  * \{

spa/include/spa/pod/compare.h

@@ -5,10 +5,6 @@
 #ifndef SPA_POD_COMPARE_H
 #define SPA_POD_COMPARE_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <stdarg.h>
 #include <errno.h>
 #include <stdint.h>
@@ -20,6 +16,10 @@ extern "C" {
 #include <spa/pod/iter.h>
 #include <spa/pod/builder.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #ifndef SPA_API_POD_COMPARE
  #ifdef SPA_API_IMPL
   #define SPA_API_POD_COMPARE SPA_API_IMPL

spa/include/spa/pod/dynamic.h

@@ -5,13 +5,13 @@
 #ifndef SPA_POD_DYNAMIC_H
 #define SPA_POD_DYNAMIC_H
 
+#include <spa/pod/builder.h>
+#include <spa/utils/cleanup.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#include <spa/pod/builder.h>
-#include <spa/utils/cleanup.h>
-
 #ifndef SPA_API_POD_DYNAMIC
  #ifdef SPA_API_IMPL
   #define SPA_API_POD_DYNAMIC SPA_API_IMPL

spa/include/spa/pod/event.h

@@ -5,12 +5,12 @@
 #ifndef SPA_EVENT_H
 #define SPA_EVENT_H
 
+#include <spa/pod/pod.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#include <spa/pod/pod.h>
-
 /**
  * \addtogroup spa_pod
  * \{

spa/include/spa/pod/filter.h

@@ -5,10 +5,6 @@
 #ifndef SPA_POD_FILTER_H
 #define SPA_POD_FILTER_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <errno.h>
 #include <stdint.h>
 #include <stddef.h>
@@ -21,6 +17,10 @@ extern "C" {
 #include <spa/pod/compare.h>
 #include <spa/pod/dynamic.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #ifndef SPA_API_POD_FILTER
  #ifdef SPA_API_IMPL
   #define SPA_API_POD_FILTER SPA_API_IMPL

spa/include/spa/pod/iter.h

@@ -5,15 +5,15 @@
 #ifndef SPA_POD_ITER_H
 #define SPA_POD_ITER_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <errno.h>
 #include <sys/types.h>
 
 #include <spa/pod/pod.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #ifndef SPA_API_POD_ITER
  #ifdef SPA_API_IMPL
   #define SPA_API_POD_ITER SPA_API_IMPL

spa/include/spa/pod/parser.h

@@ -5,16 +5,16 @@
 #ifndef SPA_POD_PARSER_H
 #define SPA_POD_PARSER_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <errno.h>
 #include <stdarg.h>
 
 #include <spa/pod/iter.h>
 #include <spa/pod/vararg.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #ifndef SPA_API_POD_PARSER
  #ifdef SPA_API_IMPL
   #define SPA_API_POD_PARSER SPA_API_IMPL

spa/include/spa/pod/pod.h

@@ -5,13 +5,13 @@
 #ifndef SPA_POD_H
 #define SPA_POD_H
 
+#include <spa/utils/defs.h>
+#include <spa/utils/type.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#include <spa/utils/defs.h>
-#include <spa/utils/type.h>
-
 /**
  * \addtogroup spa_pod
  * \{

spa/include/spa/pod/vararg.h

@@ -5,14 +5,14 @@
 #ifndef SPA_POD_VARARG_H
 #define SPA_POD_VARARG_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <stdarg.h>
 
 #include <spa/pod/pod.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /**
  * \addtogroup spa_pod
  * \{