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

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.

Reviewers: zturner, sas, xiaobai

Reviewed By: zturner

Differential Revision: https://reviews.llvm.org/D54510

llvm-svn: 346993

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

@@ -50,6 +50,17 @@ 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 = $(WINDIR)\system32\cmd.exe
+endif
+
 #----------------------------------------------------------------------
 # If TRIPLE is not defined try to set the ARCH, CC, CFLAGS, and more
 # from the triple alone