[lit] Fix shtest-shell tests on Windows

[modocache]

Summary

Tests in shtest-shell include RUN statements that attempt to
execute .sh shellscript files directly. On Windows, these would fail
with:

Could not create process (C:\path\to\llvm\utils\lit\tests\Inputs\shtest-shell/write-to-stderr.sh)
due to [Error 193] %1 is not a valid Win32 application

Instead of shellscripts, use Python scripts, and execute them with
the Python executable being used to run lit in the first place. This
succeeds on all environments.

[modocache]

The equivalent of this change was committed by @rnk in rL309200. I slightly prefer this change because the version of Python that is currently running is used to execute the shell tests, whereas rL309200 may use Python 3 to run the tests, but shell out to Python 2.

utils/lit/tests/Inputs/shtest-shell/lit.cfg

 import lit.formats
 config.name = 'shtest-shell'
 config.suffixes = ['.txt']
 config.test_format = lit.formats.ShTest()
 config.test_source_root = None
 config.test_exec_root = None
+config.substitutions.append(('%{python}', sys.executable))

utils/lit/tests/Inputs/shtest-shell/redirects.txt

 #
 # STDOUT-APPEND: is-present
 # STDOUT-APPEND: appended-line
 
 
 # Check stderr redirect (2> and 2>>).
 #
 # RUN: echo "not-present" > %t.stderr-write
-# RUN: %S/write-to-stderr.sh 2> %t.stderr-write
+# RUN: %{python} %S/write-to-stderr.py 2> %t.stderr-write
 # RUN: FileCheck --check-prefix=STDERR-WRITE < %t.stderr-write %s
 #
 # STDERR-WRITE-NOT: not-present
 # STDERR-WRITE: a line on stderr
 #
-# RUN: %S/write-to-stderr.sh 2>> %t.stderr-write
+# RUN: %{python} %S/write-to-stderr.py 2>> %t.stderr-write
 # RUN: FileCheck --check-prefix=STDERR-APPEND < %t.stderr-write %s
 #
 # STDERR-APPEND: a line on stderr
 # STDERR-APPEND: a line on stderr
 
 
 # Check combined redirect (&>).
 #
 # RUN: echo "not-present" > %t.combined
-# RUN: %S/write-to-stdout-and-stderr.sh &> %t.combined
+# RUN: %{python} %S/write-to-stdout-and-stderr.py &> %t.combined
 # RUN: FileCheck --check-prefix=COMBINED-WRITE < %t.combined %s
 #
 # COMBINED-WRITE-NOT: not-present
 # COMBINED-WRITE: a line on stdout
 # COMBINED-WRITE: a line on stderr

utils/lit/tests/Inputs/shtest-shell/write-to-stderr.py

+#!/usr/bin/env python
+
+import sys
+
+
+sys.stderr.write('a line on stderr\n')

utils/lit/tests/Inputs/shtest-shell/write-to-stderr.sh

-#!/bin/sh
-
-echo "a line on stderr" 1>&2

utils/lit/tests/Inputs/shtest-shell/write-to-stdout-and-stderr.py

+#!/usr/bin/env python
+
+import sys
+
+
+sys.stdout.write('a line on stdout\n')
+sys.stderr.write('a line on stderr\n')

utils/lit/tests/Inputs/shtest-shell/write-to-stdout-and-stderr.sh

-#!/bin/sh
-
-echo "a line on stdout"
-echo "a line on stderr" 1>&2