Define a LIB*SRCDIR for all known _LIBRARIES.

This is a follow-up to r291327 which added a LIB*DIR for all known
_LIBRARIES.

Sponsored by:	EMC / Isilon Storage Division

share/mk/bsd.libnames.mk

@@ -152,3 +152,11 @@ LDADD:=	${LDADD:N-lpthread} -lpthread
 LDADD:=	${LDADD:N-lc} -lc
 .endif
 .endif
+
+# Only do this for src builds.
+.if defined(SRCTOP)
+# Derive LIB*SRCDIR from LIB*DIR
+.for lib in ${_LIBRARIES}
+LIB${lib:tu}SRCDIR?=	${SRCTOP}/${LIB${lib:tu}DIR:S,^${OBJTOP}/,,}
+.endfor
+.endif