Windows: add CONFIG_TLS_THREAD=y and swap pthreadGC2 to libwinpthread-1.

Since GCC 4.4, MinGW has supported TLS via the __thread keyword, so
generate config-host.mak with CONFIG_TLS_THREAD=y.

MinGW now uses a new threading library libwinpthread-1.dll: install it
instead of pthreadGC2.dll.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/configure b/configure
index ef7be01..0f1acd0 100755
--- a/configure
+++ b/configure
@@ -243,6 +243,7 @@
   output_sym "CONFIG_CLOCK_GETTIME"
   output_sym "CONFIG_SCHED_IDLE"
   output_sym "CONFIG_TCP_NODELAY"
+  output_sym "CONFIG_TLS_THREAD"
   echo "CC=$CC" >> $config_host_mak
   echo "BUILD_CFLAGS=$CFLAGS -include config-host.h -D_GNU_SOURCE" >> $config_host_mak
   exit 0