Adding support for msys.

BUILD

Makefile

binding.gyp

build.yaml

config.m4

gRPC.podspec

grpc.gemspec

include/grpc/impl/codegen/port_platform.h

package.xml

src/core/lib/iomgr/tcp_server_windows.c

src/core/lib/iomgr/tcp_windows.c

src/core/lib/support/env_win32.c

src/core/lib/support/log_linux.c

src/core/lib/support/log_win32.c

src/core/lib/support/string_util_win32.c

src/core/lib/support/string_win32.c

src/core/lib/support/time_win32.c

src/core/lib/support/tmpfile_msys.c

src/core/lib/support/tmpfile_posix.c

src/core/lib/support/tmpfile_win32.c