[tools] Fix missing executable permission on downloaded tools for Unix

[zynfly]

Summary

On macOS/Linux, tools downloaded by download_tool() in src/vcpkg/tools.cpp can lack the executable bit (0644 instead of 0755), causing Permission denied (exit code 126) when vcpkg immediately attempts to run the tool to determine its version.

This affects:

• Raw binary downloads (no archive) — e.g., coscli on macOS/Linux always gets 0644 from HTTP download
• Some archive extractions — e.g., powershell-core .tar.gz loses execute permission during the extract-to-temp-then-rename process

The PowerShell Core cross-platform tool support was recently introduced in microsoft/vcpkg#49910, adding powershell-core entries for macOS and Linux to vcpkg-tools.json. This makes the permission issue more visible, as vcpkg fetch powershell-core now fails on these platforms without this fix.

The CMake-side equivalent (vcpkg_find_acquire_program.cmake) already handles this correctly via FILE_PERMISSIONS OWNER_READ OWNER_WRITE OWNER_EXECUTE ..., but the C++ download_tool() path had no such handling.

Fix

Add chmod(exe_path, 0755) before return exe_path in download_tool(), covering both the raw-binary and archive code paths in a single call. The helper is gated behind #if !defined(_WIN32) and uses Debug::println for non-fatal failure reporting.

Changes are confined to a single file (src/vcpkg/tools.cpp, +18 lines).

Test Results

Tested on macOS arm64 by comparing vcpkg fetch <tool> between the unpatched and patched binaries after clearing tool caches:

Tool	Download Type	Unpatched	Patched
coscli	raw binary	0644 — Permission denied	0755 — OK
powershell-core	.tar.gz	0644 — Permission denied	0755 — OK
node	.tar.gz	0755 — OK (preserved)	0755 — OK
azcopy	.zip	0755 — OK (preserved)	0755 — OK

• No regressions on tools that already had correct permissions (chmod is idempotent)
• Unit tests: 518/519 passed (1 pre-existing network-dependent failure unrelated to this change)

Consistency

This follows the same "chmod at placement time" pattern used throughout the vcpkg ecosystem:

• vcpkg_find_acquire_program.cmake — file(COPY ... FILE_PERMISSIONS OWNER_EXECUTE ...)
• bootstrap.sh — chmod +x before mv
• applocal.py — chmod 755 after copying dependencies

[BillyONeal]

Thank you!