RFR: 8341806: Gcc version detection failure on Alinux3

[SendaoYan]

Hi all,
There is a gcc version detection bug in `make/autoconf/toolchain.m4`.
Before this PR, the gcc version detection shell command is:

gcc --version 2>&1 | tr "\n" " " | sed -e 's/ *Copyright .*//' | sed -e 's/^.* ([1-9][0-9]*.[0-9.]*)[^0-9.].*$/\1/'

And this gcc version detection command can't work on some linux distribution such as alinux3(Alibaba Cloud Linux 3.2104).
The `gcc --version` first line output is `gcc (GCC) 10.2.1 20200825 (Alibaba 10.2.1-3.8 2.32)`, the original command get gcc  version as `2.32`, but the actual version is `10.2.1`

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Commit messages:
 - 8341806: Gcc version detection failure on Alinux3

Changes: https://git.openjdk.org/jdk/pull/21421/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21421&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341806
  Stats: 7 lines in 1 file changed: 6 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21421.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21421/head:pull/21421

PR: https://git.openjdk.org/jdk/pull/21421