NSIS perMachine fails if UAC prompt is enabled

[cwillisf]

• Version: 6.3.0

• Target: NSIS

This call to exec fails with "Error: spawn UNKNOWN" when perMachine is true and UAC prompts are enabled.

Workarounds:

• Disable UAC prompts
• Run from an elevated command prompt

Here's a partial log of the failure, running with DEBUG=*. I'd be happy to provide more logging output if it would help -- just let me know :)
NSIS-perMachine-UAC-error.txt

[develar]

Hmm... Ha! You set perMachine to true and we set RequestExecutionLevel to admin and then execute exe on your machine during build to sign uninstaller. But! To build uninstaller we don't need admin rights.