Hello,
Files like 'cpu_detect_x86_gcc', 'mmx_optimized' implement optional platform-specific optimizations . They can be compiled conditionally, and you can neglect them (my makefile for soundtouch~ for Pd does not include these routines in the builds).
For a Raspberry Pi build, the LINUX i386 section in the makefile could be copied, but without the -msse flag. Extra C flags for armv6l: -fsingle-precision-constant -mfloat-abi=hard. Architechture flags for compiler and linker: -march=armv6 -mfpu=vfp.