Create namespace for the symbols added during 15-CURRENT cycle

Reviewed by:	kib
Differential Revision:	https://reviews.freebsd.org/D41935

lib/libc/Versions.def

@@ -38,6 +38,10 @@ FBSD_1.6 {
 FBSD_1.7 {
 } FBSD_1.6;
 
+# This version was first added to 15.0-current.
+FBSD_1.8 {
+} FBSD_1.7;
+
 # This is our private namespace.  Any global interfaces that are
 # strictly for use only by other FreeBSD applications and libraries
 # are listed here.  We use a separate namespace so we can write
@@ -45,4 +49,4 @@ FBSD_1.7 {
 #
 # Please do NOT increment the version of this namespace.
 FBSDprivate_1.0 {
-} FBSD_1.7;
+} FBSD_1.8;