another attempt to fix the sh/bash confusion

meson.build

@@ -508,7 +508,7 @@ _include_search_paths = [
     '/usr/local/include',
 ] 
 foreach idir : _include_search_paths
-    _ret = run_command('sh','-c','meson/directory_exists.sh',idir).returncode()
+    _ret = run_command('meson/directory_exists.sh',idir).returncode()
     if _ret == 0
         inc_arg = idir
         _Inc_arg = '-I' + idir

meson/directory_exists.sh

-#!/bin/sh
+#!/bin/bash
 
 # return 0 if directory exists, 1 otherwise
-if [ -d "$1" ]; then
+if [[ -d "$1" ]]; then
     exit 0;
 else
     exit 1;