lpc1768: cleanup Makefile

`cpu/lpc1768/Makefile` contains many lines that don't belong into this
file, but the maybe `Makefile.include`. Either way, this Makefile is
never called with these goals.
Fix all warnings for native and qemu-i386

Missing returns, unused variables (only used for debugging), empty
translation units, missing function prototypes, and GNU extensions.
nativenet: change max packet size to 127

Real IEEE 802.15.4 transceivers have a payload of 127. Hence, for
testing - particular 6lowpan - it would make sense to have the same
limitation in nativenet. Especially to test fragmentation this is
helpful.
cpu cortex-m3_common: cleanup thread_arch.c
cpu - sam3x8e: added switch for newlib-nano specs
Merge pull request #1354 from OlegHahm/nativenet_packetsize

nativenet: change max packet size to 127
Merge pull request #1335 from Kijewski/fix-all-warnings-for-native-and-qemu-i386

Fix all warnings for native and qemu-i386
cpu - sam3x8e: fixed vtimer, added timer_set_absolute
Merge pull request #1356 from haukepetersen/fix_sam3x_newlibnano

cpu - sam3x8e: added switch for newlib-nano specs
Merge pull request #1357 from haukepetersen/fix_cortexm3_threading

cpu: cortex-m3_common: cleanup thread_arch.c
Introducing a source routing header for RPL.
Merge pull request #1218 from fabianbrandt/srh_rpl

Introducing a source routing header for RPL.
boards: removed -lto flag and cleanup for udoo&arduino due
Merge pull request #1365 from haukepetersen/fix_cortexm3_ltoflag

boards: removed -lto flag and cleanup for udoo&arduino due
Merge pull request #1358 from haukepetersen/fix_sam3x_vtimer

cpu - sam3x8e: fixed vtimer, added timer_set_absolute
Merge pull request #1187 from Kijewski/mbed_lpc1768-makefile-cleanup

lpc1768: cleanup Makefile
Initial commit of Arduino Mega2560
strip functions in atmega2560/periph and atmega_common/thread_arch.c down to prototypes

Add custom errno.h since avr-libc doesn't include one
rename board_init to main, main to o_main (inside hello-world/main.c). Fix
Makefile.include:

UART works within RIOT codebase, :)
Develop: fix invocation of avrdude