[riscv-port] RFR: 8283020: riscv: Fix configure integration

[Magnus Ihse Bursie]

The current implementation in the riscv-port modifies make/autoconf/build-aux/autoconf-* files. For legal reasons, this is not something that is allowed. Instead, we need to introduce patches in our wrapper scripts in the same directory.

This patch will restore the original contents of the autoconf-* files, and instead move this logic to the wrapper scripts. 

This PR also fixes an indentation problem in configure.

I have not been able to verify this patch, since I do not have access to riscv hardware. I believe it is sufficient and correct, but it might be the case that config.sub also needs updating. I kindly request assistance in verifying this.

(Apart from these fixes, all build changes in the riscv-port looks good to me)

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Commit messages:
 - 8283020: riscv: Fix configure integration

Changes: https://git.openjdk.java.net/riscv-port/pull/66/files
 Webrev: https://webrevs.openjdk.java.net/?repo=riscv-port&pr=66&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283020
  Stats: 17 lines in 4 files changed: 9 ins; 5 del; 3 mod
  Patch: https://git.openjdk.java.net/riscv-port/pull/66.diff
  Fetch: git fetch https://git.openjdk.java.net/riscv-port pull/66/head:pull/66

PR: https://git.openjdk.java.net/riscv-port/pull/66