Index: sys/arch/amd64/include/mcontext.h
===================================================================
RCS file: /cvsroot/src/sys/arch/amd64/include/mcontext.h,v
retrieving revision 1.19
diff -u -r1.19 mcontext.h
--- sys/arch/amd64/include/mcontext.h	15 Feb 2018 15:53:56 -0000	1.19
+++ sys/arch/amd64/include/mcontext.h	24 Dec 2019 22:14:26 -0000
@@ -84,6 +84,11 @@
 
 #define	__UCONTEXT_SIZE	784
 
+#if defined(_RTLD_SOURCE) || defined(_LIBC_SOURCE) || \
+    defined(__LIBPTHREAD_SOURCE__)
+#include <sys/tls.h>
+
+__BEGIN_DECLS
 static __inline void *
 __lwp_getprivate_fast(void)
 {
@@ -93,6 +98,9 @@
 
 	return __tmp;
 }
+__END_DECLS
+
+#endif
 
 #ifdef _KERNEL
 
Index: sys/arch/i386/include/mcontext.h
===================================================================
RCS file: /cvsroot/src/sys/arch/i386/include/mcontext.h,v
retrieving revision 1.14
diff -u -r1.14 mcontext.h
--- sys/arch/i386/include/mcontext.h	15 Feb 2018 15:53:56 -0000	1.14
+++ sys/arch/i386/include/mcontext.h	24 Dec 2019 22:14:26 -0000
@@ -113,6 +113,11 @@
 
 #define	__UCONTEXT_SIZE	776
 
+#if defined(_RTLD_SOURCE) || defined(_LIBC_SOURCE) || \
+    defined(__LIBPTHREAD_SOURCE__)
+#include <sys/tls.h>
+
+__BEGIN_DECLS
 static __inline void *
 __lwp_getprivate_fast(void)
 {
@@ -122,5 +127,8 @@
 
 	return __tmp;
 }
+__END_DECLS
+
+#endif
 
 #endif	/* !_I386_MCONTEXT_H_ */