patch 8.1.1317: output from Travis can be improved

Problem:    Output from Travis can be improved.
Solution:   Add section headers.  Handle errors better. (closes #4098)
diff --git a/configure b/configure
index 1d0c5b2..d9d99c6 100755
--- a/configure
+++ b/configure
@@ -3,4 +3,4 @@
 # This is just a stub for the Unix configure script, to provide support for
 # doing "./configure" in the top Vim directory.
 
-cd src && exec ./configure "$@"
+cd "${SRCDIR:-src}" && exec ./configure "$@"