fix .rodata._ctype_ overlap

Newer toolchain always complains:

arm-none-eabi/bin/ld: section .rodata._ctype_ loaded at
[0000000000007774,0000000000007877] overlaps section .data loaded at
[0000000000007774,000000000000779f]
collect2: error: ld returned 1 exit status
make: *** [main.bin] Error 1

We should reserve .rodata.* section as well.
fix registers may not be the same -- strexb r0,r0,[r1]
fix overlaps section
Merge pull request #4 from yyken/master

fix overlaps section
Merge from embedded2014 for bugs fixing

Conflicts:
	main.ld