[glibmm] tools/test_scripts/testheaders.sh: Require C++17

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 9a5acb6184354b086d93033e8d392d7054dcb12a
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Fri Oct 26 19:03:36 2018 +0200

    tools/test_scripts/testheaders.sh: Require C++17
    
    and fix a directory test.

 tools/test_scripts/testheaders.sh | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)
---
diff --git a/tools/test_scripts/testheaders.sh b/tools/test_scripts/testheaders.sh
index 5780d7fd..7d618419 100755
--- a/tools/test_scripts/testheaders.sh
+++ b/tools/test_scripts/testheaders.sh
@@ -18,8 +18,7 @@ function usage() {
   exit 1
 }
 
-#extra_gcc_args=-std=c++11
-extra_gcc_args=
+extra_gcc_args=-std=c++17
 
 # Search for directories to include in CFLAGS.
 idirs=""
@@ -56,7 +55,7 @@ shift
 # Search for more directories to include in CFLAGS.
 for i in "$@"
 do
-  if [ -d "$1" ]
+  if [ -d "$i" ]
   then
     idirs+=" -I$i"
   fi