Fix a number of header files with mismatched 'extern C {' and '}'

include/nuttx/arch.h

@@ -2294,9 +2294,8 @@ void arch_sporadic_resume(FAR struct tcb_s *tcb);
 #endif
 
 #undef EXTERN
-#ifdef __cplusplus
+#if defined(__cplusplus)
 }
 #endif
 
 #endif /* __INCLUDE_NUTTX_ARCH_H */
-

include/nuttx/binfmt/symtab.h

@@ -90,4 +90,9 @@ void exec_getsymtab(FAR const struct symtab_s **symtab, FAR int *nsymbols);
 
 void exec_setsymtab(FAR const struct symtab_s *symtab, int nsymbols);
 
+#undef EXTERN
+#if defined(__cplusplus)
+}
+#endif
+
 #endif /* __INCLUDE_NUTTX_BINFMT_SYMTAB_H */