RFR: 8343883: Cannot resolve user specified toolchain-path for lld after JDK-8338304 [v2]

[SendaoYan]

> Hi all,
> After [JDK-8338304](https://bugs.openjdk.org/browse/JDK-8338304), below configure command will generate failure `error: Could not find required tool for LLD`. The lld linker located in path which config with option `--with-toolchain-path`, but the check `UTIL_REQUIRE_PROGS(LLD, lld)` introduced by [JDK-8338304](https://bugs.openjdk.org/browse/JDK-8338304) was unable to find the lld. This PR add the condition to deal with user specidied `--with-toolchain-path` to find the correct lld fullpath. The change has beeen verified locally, trivial fix, the risk is low.
> 
> 
> bash configure --with-jobs=128 --with-debug-level=release --enable-unlimited-crypto --with-jvm-variants=server --with-version-opt=f4008968 --with-zlib=system --with-toolchain-type=clang --with-toolchain-path=/home/yansendao/software/acc/x86_64/bin

SendaoYan has updated the pull request incrementally with one additional commit since the last revision:

  lookup $TOOLCHAIN_PATH:$PATH

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Changes:
  - all: https://git.openjdk.org/jdk/pull/21999/files
  - new: https://git.openjdk.org/jdk/pull/21999/files/6f513a3a..216a0d4b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21999&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21999&range=00-01

  Stats: 5 lines in 1 file changed: 0 ins; 4 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21999.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21999/head:pull/21999

PR: https://git.openjdk.org/jdk/pull/21999