keg_relocate: swap env var

[dawidd6]

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This might cause trouble for us in homebrew-core.

[BrewTestBot]

Review period will end on 2021-07-06 at 00:00:00 UTC.

[iMichka]

We suspect that this will fix the error we got while bottling swig in homebrew-core for Linux:

2021-07-04T08:10:39.2645358Z �[34m==>�[0m �[1mbrew linkage --test swig�[0m
2021-07-04T08:10:40.4584391Z �[31m==>�[0m �[1m�[31mFAILED�[0m�[0m
2021-07-04T08:10:40.4584949Z Missing libraries:
2021-07-04T08:10:40.4585497Z   unexpected (libgcc_s.so.1)
2021-07-04T08:10:40.4586085Z   unexpected (libstdc++.so.6)
2021-07-04T08:10:40.4586463Z 
2021-07-04T08:10:40.4587344Z �[34m==>�[0m �[1mbrew install --only-dependencies --include-test swig�[0m
2021-07-04T08:11:14.0968351Z �[34m==>�[0m �[1mbrew test --verbose swig�[0m
2021-07-04T08:11:16.8242005Z �[31m==>�[0m �[1m�[31mFAILED�[0m�[0m
2021-07-04T08:11:16.8244170Z �[32m==>�[0m �[1mTesting swig�[0m
2021-07-04T08:11:16.8245327Z �[34m==>�[0m �[1m/home/linuxbrew/.linuxbrew/Cellar/swig/4.0.2/bin/swig -ruby test.i�[0m
2021-07-04T08:11:16.8246715Z /home/linuxbrew/.linuxbrew/Cellar/swig/4.0.2/bin/swig: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory
2021-07-04T08:11:16.8248080Z �[31mError:�[0m swig: failed
2021-07-04T08:11:16.8248823Z An exception occurred within a child process:
2021-07-04T08:11:16.8250110Z   BuildError: Failed executing: /home/linuxbrew/.linuxbrew/Cellar/swig/4.0.2/bin/swig -ruby test.i

[BrewTestBot]

Review period skipped due to critical label.

[iMichka]

It worked!