pass -nostartfiles to the linker

.cargo/config

@@ -0,0 +1,11 @@
+[target.thumbv6m-none-eabi]
+rustflags = ["-C", "link-arg=-nostartfiles"]
+
+[target.thumbv7m-none-eabi]
+rustflags = ["-C", "link-arg=-nostartfiles"]
+
+[target.thumbv7em-none-eabi]
+rustflags = ["-C", "link-arg=-nostartfiles"]
+
+[target.thumbv7em-none-eabihf]
+rustflags = ["-C", "link-arg=-nostartfiles"]