restore additional info about the potential cause of find_program failing

Before commit f08eed37cb we also mentioned
that it might not be executable.

mesonbuild/interpreter/interpreter.py

@@ -1448,7 +1448,7 @@ external dependencies (including libraries) must go to "dependencies".''')
             if not silent:
                 mlog.log('Program', mlog.bold(progobj.get_name()), 'found:', mlog.red('NO'))
             if required:
-                m = 'Program {!r} not found'
+                m = 'Program {!r} not found or not executable'
                 raise InterpreterException(m.format(progobj.get_name()))
             return progobj
 

test cases/failing/101 no glib-compile-resources/test.json

@@ -1,7 +1,7 @@
 {
   "stdout": [
     {
-      "line": "test cases/failing/101 no glib-compile-resources/meson.build:8:0: ERROR: Program 'glib-compile-resources' not found"
+      "line": "test cases/failing/101 no glib-compile-resources/meson.build:8:0: ERROR: Program 'glib-compile-resources' not found or not executable"
     }
   ]
 }