Add QNX and OSX to known platforms

[hofbi]

What type of PR is this?

Uncomment one line below and remove others.

Bug fix

What package or component does this PR mostly affect?

language/go
cmd/gazelle

What does this PR do? Why is it needed?

Adding more known platforms to avoid issue reported in #1735.

Which issues(s) does this PR fix?

Fixes #1735

Other notes for review

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[hofbi]

@fmeum Could you take a look at this one?

[darkrift]

While working on another change in rules_go, I stumbled upon this PR because of the following error in our repository:

ERROR: /private/var/tmp/_bazel_rlavoie/a0035c26b826a3ecd42a2733d971df53/external/rules_go~/go/platform/BUILD.bazel: no such target '@@rules_go~//go/platform:osx': target 'osx' not declared in package 'go/platform' defined by /private/var/tmp/_bazel_rlavoie/a0035c26b826a3ecd42a2733d971df53/external/rules_go~/go/platform/BUILD.bazel
ERROR: /private/var/tmp/_bazel_rlavoie/a0035c26b826a3ecd42a2733d971df53/external/rules_go~/go/platform/BUILD.bazel: no such target '@@rules_go~//go/platform:qnx': target 'qnx' not declared in package 'go/platform' defined by /private/var/tmp/_bazel_rlavoie/a0035c26b826a3ecd42a2733d971df53/external/rules_go~/go/platform/BUILD.bazel
ERROR: /private/var/tmp/_bazel_rlavoie/a0035c26b826a3ecd42a2733d971df53/external/gazelle~~go_deps~com_github_prometheus_client_golang/prometheus/BUILD.bazel:3:11: errors encountered resolving select() keys for @@gazelle~~go_deps~com_github_prometheus_client_golang//prometheus:prometheus
ERROR: /private/var/tmp/_bazel_rlavoie/a0035c26b826a3ecd42a2733d971df53/external/gazelle~~go_deps~org_golang_google_grpc/internal/syscall/BUILD.bazel:3:11: errors encountered resolving select() keys for @@gazelle~~go_deps~org_golang_google_grpc//internal/syscall:syscall