Resolve relative paths in sdk build scripts.

E.g. such command:
./src/tools_webrtc/ios/build_ios_libs.sh --build_config debug \
     --arch arm64 --output-dir ./out/ios_debug/

Failed before this CL, because build files actually saved into different
location and when attempted to copy to destinatoin dir error occurred.

No-Presubmit: True
Bug: None
Change-Id: Ib7dd23a95cc81873c0eb61cc3c6bf51573936f78
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/206810
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33275}

tools_webrtc/android/build_aar.py

@@ -54,9 +54,11 @@ def _ParseArgs():
     parser = argparse.ArgumentParser(description='libwebrtc.aar generator.')
     parser.add_argument(
         '--build-dir',
+        type=os.path.abspath,
         help='Build dir. By default will create and use temporary dir.')
     parser.add_argument('--output',
                         default='libwebrtc.aar',
+                        type=os.path.abspath,
                         help='Output file of the script.')
     parser.add_argument(
         '--arch',