SpeexDSP-1.2.1 release

- CI: add gitlab CI integration
- fixed-point: Remove unused MULT16_32_Q1[1-4] macros and inlines
- fixed-point: don't truncate 32-bit arg to MULT16_32_Q15
- fixed-point resample: remove 1-bit shift right before interpolation
- fixed-point: introduce MULT16_32_32 to handle unexpected types in MULT16_32_Q15
- Fix incorrect macro names in arch.h
- Remove unused stack_alloc.h
- autotools: do not use deprecated macros