Updated DSP library + build system changes

Updated CMSIS DSP to latest version (CMSIS-SP-00300-r3p2-00rel1.zip)
Build system changes to be able to preprocess assembler sources before compiling them:

- GCC: use gcc '-x assembler-with-cpp'
- ARM: preprocess first, then assemble (two separate commands)
- IAR: added macro definitions and include directories to the assembler command line

Removed CORTEX_ARM_SUPPORT restriction for the DSP libraries.
Tested: LPC1768 with ARM, GCC_ARM and IAR, LPC11U24 with ARM.