stm32f1x_cl: Add initial support for STM32F1x connectivity line

This currently supports the stm32f107, but support will be added for
the F105 shortly (missing a linker script and I can't properly test
without a devkit).

cpu/arm/stm32f1x_cl/mtarch.h

@@ -0,0 +1,13 @@
+/*
+ * Implementation of multithreading in ARM Cortex-M3. To be done.
+ */
+
+
+#ifndef __MTARCH_H__
+#define __MTARCH_H__
+
+struct mtarch_thread {
+  short mt_thread;
+};
+
+#endif /* __MTARCH_H__ */