[build system] removed detection/support for old non-multilib toolchains
* stm32: removed fix-cortex-m3-ldrd from flags: is already enabled with -mcpu=cortex-m3
* lpc21: shoul actually also still work with the really old arm-elf compiler, although not recommended
* While here clean up a bit more and move some more stuff to the common makefile

This fix should fix compilation of stm32 firmwares with other toolchains
then the one provided by paparazzi. Tested with gcc-arm-embedded
(https://launchpad.net/gcc-arm-embedded) 4_7-2012q4 on mac os x and ubuntu 12.04.

The toolchain is more optimized for arm cortex m and r series cpus.
[stm32] removed some more old debug targets in the makefile