cmd/compile: emit sensible go_asm.h consts for big ints
Currently, the compiler will emit any const that doesn't fit in an
int64 to go_asm.h like
#define const_stackPreempt constant.intVal{val:(*big.Int)(0xc000c06c40)}
This happens because dumpasmhdr formats the constant.Value using the
verb "%#v". Since constant.Value doesn't implement the GoString()
method, this just prints the Go-syntax representation of the value.
This happens to work for small integer constants, which go/constant
represents directly as an int64, but not for integer constants that
don't fit in an int64, which go/constant represents as a big.Int.
Make these constants usable by changing the formatting verb to "%v",
which will call the String() method, giving a reasonable result in all
cases.
Change-Id: I365eeb88c8acfc43ff377cc873432269bde3f541
Reviewed-on: https://go-review.googlesource.com/c/go/+/359954
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>