Expose symbols on macos in the xplat pytorch stack (#9819)

Summary:
X-link: pytorch/pytorch#150487


Had to revert D71321310 because it affected way too many targets and build sizes.

These changes should expose just enough symbols to be buildable in arvr mode on macOS. Could potentially make narrow it down even more by avoiding eg `get_pt_compiler_flags`

Differential Revision: D72255474

Author: stepanhruda

shim_et/xplat/executorch/build/runtime_wrapper.bzl

@@ -112,6 +112,11 @@ def _patch_build_mode_flags(kwargs):
         # @oss-disable: "ovr_config//build_mode:code-coverage": ["-D__ET_BUILD_MODE_COV=1"],
     })
 
+    kwargs["compiler_flags"] = kwargs["compiler_flags"] + select({
+            "DEFAULT": [],
+            "ovr_config//os:macos": ["-fvisibility=default"],
+    })
+
     return kwargs
 
 def _patch_test_compiler_flags(kwargs):