[Build System: build-script] Remove the tar module from swift_build_support.

The single function it provided to archive a source diretory has been moved to build-script which was the only caller.

Author: Ross Bayer

utils/build-script

@@ -30,7 +30,6 @@ from swift_build_support.swift_build_support import (
     diagnostics,
     products,
     shell,
-    tar,
     targets,
     workspace
 )
@@ -89,6 +88,25 @@ def print_xcodebuild_versions(file=sys.stdout):
     file.flush()
 
 
+def tar(source, destination):
+    """
+    Create a gzip archive of the file at 'source' at the given
+    'destination' path.
+    """
+    # We do not use `tarfile` here because:
+    #  - We wish to support LZMA2 compression while also supporting Python 2.7.
+    #  - We wish to explicitly set the owner and group of the archive.
+    args = ['tar', '-c', '-z', '-f', destination]
+
+    if platform.system() != 'Darwin' and platform.system() != 'Windows':
+        args += ['--owner=0', '--group=0']
+
+    # Discard stderr output such as 'tar: Failed to open ...'. We'll detect
+    # these cases using the exit code, which should cause 'shell.call' to
+    # raise.
+    shell.call(args + [source], stderr=shell.DEVNULL)
+
+
 class BuildScriptInvocation(object):
 
     """Represent a single build script invocation."""
@@ -1169,8 +1187,8 @@ def main_normal():
         # run `tar` without the leading '/' (we remove it ourselves to keep
         # `tar` from emitting a warning).
         with shell.pushd(args.install_symroot):
-            tar.tar(source=prefix.lstrip('/'),
-                    destination=args.symbols_package)
+            tar(source=prefix.lstrip('/'),
+                destination=args.symbols_package)
 
     return 0