PM prepares the ARM64 build environment again inside callers that already
carry a matching developer environment. It is reused as-is, including PATH
order, and a Git Bash caller puts coreutils' link.exe first, so the guard
aborted setup ("MSVC link.exe is shadowed by ...\Git\usr\bin\link.exe").
VsDevCmd's VCToolsInstallDir names the MSVC linker exactly, whichever way
the environment was obtained. PATH order stays the caller's.
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