BUT, there’s nothing I can find in any of the condif.sh scripts, or anywhere else as to how “CONFIG_TARGET_ARM_SA11X0 = 1” points the install to anything useful, and config.sh or anything else.

Look at the default Makefile in perlsrc/Cross:

## Optimisation work
ifeq ($(ARCH),arm)
 ifdef CONFIG_TARGET_ARM_SA11X0
   ifndef Architecture
     Architecture = armv4l-strongarm
   endif
   FULL_OPTIMIZATION += -march=armv4 -mtune=strongarm1100 -mapcs-32
   OPTIMIZATION += -march=armv4 -mtune=strongarm1100 -mapcs-32
 endif
endif
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I haven't done cross-compiling yet, so I don't know how this flag is generated - but at least that's where the flag does something useful ;-)