sudo apt install gcc-multilib g++-multilib
https://github.com/libsdl-org/SDL-1.2/releases/tag/release-1.2.15
./configure --build=i686-pc-linux-gnu CFLAGS=-m32 CXXFLAGS=-m32 LDFLAGS=-m32
nano Makefile
CC=$(CROSS_COMPILE)gcc -m32 # gcc or g++
......
LDFLAGS+=-Wl,--gc-sections,-m,elf_i386