glib: fix g-ir-scanner PATH precedence.

[ewtoombs]

The staging g-ir-scanner must be preferred over the system's g-ir-scanner. A mismatch in the versions, for example, will cause the build to fail.

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[carlocab]

The staging g-ir-scanner must be preferred over the system's g-ir-scanner. A mismatch in the versions, for example, will cause the build to fail.

The system's g-ir-scanner should already not be on PATH in the build environment. How did you install the conflicting g-ir-scanner?

[ewtoombs]

I don't know why g-ir-scanner is sometimes in the PATH already, but it can be.
This is what caused the build to fail for me.
The fix is simple enough.
I see no reason why it can't be applied.

[carlocab]

I see no reason why it can't be applied.

One reason is that the choice to append rather than prepend to PATH in 19b6bb1 could've been deliberate.

Another is that it appears, from your description so far, that there is an underlying bug that's causing your build failure, and applying this change just masks that bug. We should fix it instead of try to hide the symptoms.

How did you install the conflicting g-ir-scanner? What is the output of your brew config?

[cho-m]

There does seem to be a scenario where Linux can use a system copy as the sanitized PATH includes /usr/bin. On macOS, I don't think this would happen.

I'm okay with modification as the staging bin directory should only have g-ir-* executables.