Wrong link flags when compiling with Bazel and clang-cl

[oakad]

When compiling with clang-cl toolchain (@bazel_tools//tools/cpp:clang-cl), wrong link flags will be set.

clang-cl is an important toolchain in particular for deep nested schemas, because it does not suffer from MAX_PATH limitations the normal cl toolchain has.

protobuf/build_defs/cpp_opts.bzl

Lines 26 to 40 in 450d24c

	LINK_OPTS = select({
	"//build_defs:config_android": [],
	"//build_defs:config_android-stlport": [],
	"//build_defs:config_android-libcpp": [],
	"//build_defs:config_android-gnu-libstdcpp": [],
	"//build_defs:config_android-default": [],
	"//build_defs:config_msvc": [
	# Suppress linker warnings about files with no symbols defined.
	"-ignore:4221",
	],
	"//conditions:default": [
	"-lpthread",
	"-lm",
	],
	})