cmd/compile: internal compiler error len larger than cap for OSLICEHEADER [1.25 backport]

[gopherbot]

@cuonglm requested issue #77919 to be considered for backport to the next 1.25 minor release.

@gopherbot Please backport this to go1.25 and go1.26 branch.

This causes an ICE when compiling certain programs with non-constant argument to make.