os/mac/keg: print stderr on codesign failure

[Bo98]

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I've not tested this code (I don't have an Apple Silicon Mac anymore).

[BrewTestBot]

Review period will end on 2021-02-11 at 23:13:08 UTC.

[MikeMcQuaid]

Good idea 👏🏻

[BrewTestBot]

Review period skipped due to critical label.

[dtrodrigues]

Looks great:

$ brew install openjdk
==> Downloading https://homebrew.bintray.com/bottles/openjdk-15.0.1.arm64_big_sur.bottle.1.tar.gz
==> Downloading from https://d29vzk4ow07wi7.cloudfront.net/64da5d70d63d617def59e16bd411f236b822626f130a6b16576eb9eb5bc8519a?response-content-disposition=attachment%3Bfilename%3D%22openjdk-15.0.1.arm64_big
######################################################################## 100.0%
==> Pouring openjdk-15.0.1.arm64_big_sur.bottle.1.tar.gz
Error: Failed applying an ad-hoc signature to /opt/homebrew/Cellar/openjdk/15.0.1/libexec/openjdk.jdk/Contents/MacOS/libjli.dylib:
/opt/homebrew/Cellar/openjdk/15.0.1/libexec/openjdk.jdk/Contents/MacOS/libjli.dylib: replacing existing signature
/opt/homebrew/Cellar/openjdk/15.0.1/libexec/openjdk.jdk/Contents/MacOS/libjli.dylib: resource fork, Finder information, or similar detritus not allowed