https://jira.mongodb.org/browse/SERVER-94430 Upstream respond:

> we intentionally do not ingest the environment PATH as this makes build
> reproducibility and hermiticity much harder. Instead, you should set the
> absolute paths to the tools you want to use on the command line, instead of
> relying on the PATH.

Gentoo bug https://bugs.gentoo.org/829340

In Gentoo, we have LLVM slotted and we put clang in /usr/lib/llvm/18/bin (or
whatever), not in /usr/bin, and if upstream strip PATH and construct it
themselves, they surely won't contain this location.

So we add PATH backup for scons.
diff --git a/SConstruct b/SConstruct
index 3d831c9..f07feeb 100644
--- a/SConstruct
+++ b/SConstruct
@@ -1201,7 +1201,7 @@ envDict = dict(BUILD_ROOT=buildDir,
 if get_option('build-tools') == 'next':
     SCons.Tool.DefaultToolpath.insert(0, os.path.abspath('site_scons/site_tools/next'))
 
-env = Environment(variables=env_vars, **envDict)
+env = Environment(variables=env_vars, ENV={'PATH': os.environ['PATH']}, **envDict)
 del envDict
 
 if get_option('cache-signature-mode') == 'validate':