patch 8.0.0464: can't find executable name on Solaris and FreeBSD

Problem:    Can't find executable name on Solaris and FreeBSD.
Solution:   Check for "/proc/self/path/a.out". (Danek Duvall) And for
            "/proc/curproc/file".
diff --git a/src/config.h.in b/src/config.h.in
index a9bcf1e..f8a23ed 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -446,8 +446,8 @@
 /* Define if fcntl()'s F_SETFD command knows about FD_CLOEXEC */
 #undef HAVE_FD_CLOEXEC
 
-/* Define if /proc/self/exe can be read */
-#undef HAVE_PROC_SELF_EXE
+/* Define if /proc/self/exe or similar can be read */
+#undef PROC_EXE_LINK
 
 /* Define if you want Cygwin to use the WIN32 clipboard, not compatible with X11*/
 #undef FEAT_CYGWIN_WIN32_CLIPBOARD