cmd/link/internal/ld: assign temporary addresses to per-package text

If trampolines may be required, the current text addressing second
pass resets all assigned addresses, before assigning addresses and
laying down trampolines in a linear fashion. However, this approach
means that intra-package calls are to a symbol that has not yet
been assigned an address, when the symbol is ahead of the current
function.

In the case of RISC-V the JAL instruction is limited to +/-1MiB.
As such, if a call is to a symbol with no address currently assigned,
we have to assume that a trampoline will be required. During the
relocation phase we can fix up and avoid trampolines in some cases,
however this results in unused trampolines that are still present
in the binary (since removing them would change text addresses).

In order to significantly reduce the number of unused trampolines,
assign temporary addresses to functions within the same package,
based on the maximum number of trampolines that may be required by
a function. This allows for better decisions to be made regarding
the requirement for intra-package trampolines, as we reset the
addressing for a function, assign its final address and lay down
any resulting trampolines.

This results in ~2,300 unused trampolines being removed from the
Go binary and ~5,600 unused trampolines being removed from the
compile binary, on linux/riscv64.

This reapplies CL 349650, however does not pass big to assignAddress
when assigning temporary addresses, as this can result in side
effects such as section splitting.

Change-Id: Id7febdb65d962d6b1297a91294a8dc27c94d8696
Reviewed-on: https://go-review.googlesource.com/c/go/+/534760
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Joel Sing <joel@sing.id.au>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

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