RFR: 8339128: Cannot resolve user specified tool properly after JDK-8338304

[Magnus Ihse Bursie]

On Fri, 1 Nov 2024 00:08:56 GMT, Jiangli Zhou <jiangli at openjdk.org> wrote:

> Please review this PR that fixes JDK build configure failure when using clang after JDK-8338304:
> 
> 
> Found candidate GCC installation: <snip>
> Selected GCC installation: <snip>
> ...
> clang: error: unsupported option '-V -static-libgcc'
> configure:85215: $? = 1
> configure:85204: <snip> -qversion >&5
> clang: error: unknown argument '-qversion'; did you mean '--version'?
> ...
> 
> 
> Tool from Clang GCC installation is being picked up unexpectedly (JDK build configured with `--with-toolchain-type=clang`). With this fix, it avoids `UTIL_REQUIRE_PROGS(LLD, lld)` if user supplies compiler toolchain. The user supplied compiler toolchain is used by setting `CXX=<user_specified_path_to_tools_script>` during configuration.

make/autoconf/toolchain.m4 line 448:

> 446:       fi
> 447:     fi
> 448:     USE_USER_SUPPLIED_COMPILER=true

This code is called for both CC and CXX. So if you run like `configure CC=foo` (but not with `CXX=bar` at the same time), the value of this variable will be determined by which check happens to be run first by configure.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21817#discussion_r1825959316