re PR go/89321 (cross build with riscv64 gccgo compilation failed due to assert in constructor_expression)

	PR go/89321
    compiler: copy has_padding field from converted struct
    
    Test case is https://golang.org/cl/162617.
    
    Fixes https://gcc.gnu.org/PR89321
    
    Reviewed-on: https://go-review.googlesource.com/c/162618

From-SVN: r268904