Force c++14 when running tests on Windows.

VS 2015 and higher begin making use of c++14 in their standard
library headers.  As such, -std=c++11 makes it so you can't compile
trivial programs.  Bump this to -std=c++14 when this situation is
detected.

llvm-svn: 281420

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

@@ -303,6 +303,7 @@ ifeq "$(OS)" "Windows_NT"
 		CXXFLAGS += -D_HAS_EXCEPTIONS=0
 		ifeq "$(VisualStudioVersion)" "14.0"
 			CXXFLAGS += -fms-compatibility-version=19.0
+			override CXXFLAGS := $(subst -std=c++11,-std=c++14,$(CXXFLAGS))
 		endif
 		# The MSVC linker doesn't understand long section names
 		# generated by the clang compiler.