newlib: Fix header issues with C++ guards and implicit inclusion

* Added C++ sentinels if missed
* Used #pragma once, removed macro's with leading underscores
* Updated copyright checker to allow "BSD-2-Clause-FreeBSD AND
Apache-2.0" for newlib files
* Fixed minor compilation issues/implicit inclusions

components/newlib/platform_include/sys/reent.h

@@ -8,8 +8,16 @@
 
 #include_next<sys/reent.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /* This function is not part of the newlib API, it is defined in libc/stdio/local.h
  * There is no nice way to get __cleanup member populated while avoiding __sinit,
  * so extern declaration is used here.
  */
 extern void _cleanup_r(struct _reent* r);
+
+#ifdef __cplusplus
+}
+#endif

components/newlib/platform_include/sys/un.h

@@ -3,8 +3,11 @@
  *
  * SPDX-License-Identifier: Apache-2.0
  */
-#ifndef _ESP_PLATFORM_SYS_UN_H_
-#define _ESP_PLATFORM_SYS_UN_H_
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 #define	AF_UNIX		1		/* local to host (pipes) */
 
@@ -13,4 +16,6 @@ struct sockaddr_un {
             char                     sun_path[108];             /*path name */
 };
 
-#endif // _ESP_PLATFORM_SYS_UN_H_
+#ifdef __cplusplus
+}
+#endif

components/newlib/platform_include/sys/unistd.h

@@ -4,20 +4,19 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#pragma once
 
-#ifndef _ESP_SYS_UNISTD_H
-#define _ESP_SYS_UNISTD_H
+#include <sys/types.h>
+
+#include_next <sys/unistd.h>
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#include_next <sys/unistd.h>
-
 int truncate(const char *, off_t __length);
 int gethostname(char *__name, size_t __len);
 
 #ifdef __cplusplus
 }
 #endif
-#endif /* _SYS_UNISTD_H */