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/endian.h

@@ -50,6 +50,10 @@
  */
 #include <machine/endian.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /*
  * General byte order swapping functions.
  */
@@ -198,3 +202,7 @@ le64enc(void *pp, uint64_t u)
 	le32enc(p, (uint32_t)(u & 0xffffffffU));
 	le32enc(p + 4, (uint32_t)(u >> 32));
 }
+
+#ifdef __cplusplus
+}
+#endif