In the Makefile, comment out the lines:

CPPFLAGS += -DPNGCRUSH_USE_ARM_NEON
CPPFLAGS += -DPNGCRUSH_USE_MPS_MSA
CPPFLAGS += -DPNGCRUSH_USE_INTEL_SSE -DPNG_INTEL_SSE
CPPFLAGS += -DPNGCRUSH_USE_POWERPC_VSX

In zutil.h, comment out the line:

typedef long ptrdiff_t;

Then execute one of:

make "OPTIONS=-mcpu=G3 -mtune=G3 -mmacosx-version-min=10.1"
make "OPTIONS=-mcpu=7400 -mtune=7400 -mmacosx-version-min=10.1"
make "OPTIONS=-mcpu=7450 -mtune=7450 -mmacosx-version-min=10.1"
make "OPTIONS=-mcpu=G5 -mtune=G5 -mmacosx-version-min=10.1"