Force SHELL to be cmd.exe on Windows for the test suite

[lanza]

Summary

Windows make will search for other shells and choose those over cmd
if available (e.g. C:\cygdrive\bin\sh.exe). This shell has numerous
issues with path handling (/ vs \\ vs \ and C:). So default to using
cmd.exe which is known to work.

[lanza]

I ran a subset of the test suite (around 350 tests) and found that there are 0 cases where a pass occurred with C:\cygwin\bin\sh.exe but not with C:\windows\system32\cmd.exe. So this should be safe.

[zturner]

lgtm after fixing the one comment.

packages/Python/lldbsuite/test/make/Makefile.rules

61

Can you use $(WINDIR) here instead of hardcoding C:\Windows?

packages/Python/lldbsuite/test/make/Makefile.rules

 ifneq (,$(findstring windows32,$(HOST_OS)))
   HOST_OS = Windows_NT
 endif
 ifeq "$(OS)" ""
   OS = $(HOST_OS)
 endif
 
 #----------------------------------------------------------------------
+# If OS is Windows, force SHELL to be cmd
+#
+# Some versions of make on Windows will search for other shells such as
+# C:\cygwin\bin\sh.exe. This shell fails for numerous different reasons
+# so default to using cmd.exe.
+#----------------------------------------------------------------------
+ifeq "$(OS)" "Windows_NT"
+  SHELL = C:\windows\system32\cmd.exe
+endif
+
+#----------------------------------------------------------------------
 # If TRIPLE is not defined try to set the ARCH, CC, CFLAGS, and more
 # from the triple alone
 #----------------------------------------------------------------------
 ARCH_CFLAGS :=
 ifneq "$(TRIPLE)" ""
   triple_space = $(subst -, ,$(TRIPLE))
   ARCH =$(word 1, $(triple_space))
   TRIPLE_VENDOR =$(word 2, $(triple_space))