fix all missing instances of __cplusplus checks/extern "C" in headers

patch by Arvid Picciani (aep)

include/sys/mount.h

@@ -1,6 +1,10 @@
 #ifndef _SYS_MOUNT_H
 #define _SYS_MOUNT_H
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #include <sys/ioctl.h>
 
 #define BLKROSET   _IO(0x12, 93)
@@ -43,4 +47,8 @@ int mount(const char *, const char *, const char *, unsigned long, const void *)
 int umount(const char *);
 int umount2(const char *, int);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif