[avro-c] no absolute paths

[autoantwort]

For #20469

[JonLiu1993]

@autoantwort ,Thanks for posting this issue, could you please take a look:

There should be no empty directories in D:\packages\avro-c_x86-windows
The following empty directories were found:

    D:/packages/avro-c_x86-windows/debug/lib/pkgconfig
    D:/packages/avro-c_x86-windows/lib/pkgconfig

If a directory should be populated but is not, this might indicate an error in the portfile.
If the directories are not needed and their creation cannot be disabled, use something like this in the portfile to remove them:

    file(REMOVE_RECURSE "${CURRENT_PACKAGES_DIR}\debug\lib\pkgconfig" "${CURRENT_PACKAGES_DIR}\lib\pkgconfig")

[BillyONeal]

Thanks for removing broken pkgconfigs!