[gdm] build: Fix double --enable-enable in previous commit

[Colin Walters <walters src gnome org>]

commit fd79a98717284435414633caf9a358c28bb6bf57
Author: Colin Walters <walters verbum org>
Date:   Mon Jun 1 21:10:42 2015 -0400

    build: Fix double --enable-enable in previous commit
    
    Noticed this because the Continuous smoketest started timing out.

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 427f41a..426566d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -178,7 +178,7 @@ AC_SUBST(dmconfdir)
 dnl ---------------------------------------------------------------------------
 dnl - Configure arguments
 dnl ---------------------------------------------------------------------------
-AC_ARG_ENABLE(enable-gdm-xsession,
+AC_ARG_ENABLE(gdm-xsession,
               AS_HELP_STRING([--enable-gdm-xsession],
                              [Enable installing the gdm Xsession file @<:@default=no@:>@]),,
               enable_gdm_xsession=no)