lm4f: Fix problems with example Makefile.include

Fix three distinct issues were present with
examples/lm4f/Makefile.include:
1. Architecture flags were not being passed to the linker. This caused the linker
to link against the wrong libraries when trying to use any C library, causing
hard faults.
2. -lc and -lnosys were not linked against. Try using printf() without -lnosys
3. The makefile erroneously specified -mcpu=cortex-m3 instead of m4.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>