initialize default_inc_excludes_dot to '' like every variable

Handling of the default is done further down.

diff --git a/Configure b/Configure
index 07dfb7c..e32d18c 100755 (executable)
--- a/Configure
+++ b/Configure
@@ -937,7 +937,7 @@ d_wcstombs=''
 d_wcsxfrm=''
 d_wctomb=''
 d_writev=''
-default_inc_excludes_dot='undef'
+default_inc_excludes_dot=''
 dlext=''
 bin_ELF=''
 cccdlflags=''