--shared-libs should be a common argument

Summary:
X-link: https://github.com/facebookincubator/zstrong/pull/848

Because it should work with `show-inst-dir`, otherwise we can't
calculate the right project hash.

Reviewed By: chadaustin

Differential Revision: D58011867

fbshipit-source-id: d8960b4a993efbada8e27584e56976279fcd6b43

build/fbcode_builder/getdeps.py

@@ -810,12 +810,6 @@ class BuildCmd(ProjectCmdBase):
             ),
             action="append",
         )
-        parser.add_argument(
-            "--shared-libs",
-            help="Build shared libraries if possible",
-            action="store_true",
-            default=False,
-        )
         parser.add_argument(
             "--free-up-disk",
             help="Remove unused tools and clean up intermediate files if possible to maximise space for the build",
@@ -1326,6 +1320,12 @@ def parse_args():
         action="store_false",
         dest="facebook_internal",
     )
+    add_common_arg(
+        "--shared-libs",
+        help="Build shared libraries if possible",
+        action="store_true",
+        default=False,
+    )
     add_common_arg(
         "--allow-system-packages",
         help="Allow satisfying third party deps from installed system packages",