Expose symbols on macos in the xplat pytorch stack (pytorch#150487)

Summary:
Pull Request resolved: pytorch#150487

X-link: pytorch/executorch#9819

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

buckbuild.bzl

@@ -194,6 +194,9 @@ def get_pt_compiler_flags():
     return select({
         "DEFAULT": _PT_COMPILER_FLAGS,
         "ovr_config//compiler:cl": windows_convert_gcc_clang_flags(_PT_COMPILER_FLAGS),
+    }) + select({
+        "DEFAULT": [],
+        "ovr_config//os:macos": ["-fvisibility=default"],
     })
 
 _PT_COMPILER_FLAGS = [
@@ -228,6 +231,9 @@ ATEN_COMPILER_FLAGS = [
     # Not supported by clang on Windows
     "DEFAULT": ["-fPIC"],
     "ovr_config//compiler:clang-windows": [],
+}) + select({
+    "DEFAULT": [],
+    "ovr_config//os:macos": ["-fvisibility=default"],
 })
 
 def get_aten_compiler_flags():
@@ -982,6 +988,10 @@ def define_buck_targets(
     fb_xplat_cxx_library(
         name = "torch_mobile_headers",
         header_namespace = "",
+        compiler_flags = select({
+            "DEFAULT": [],
+            "ovr_config//os:macos": ["-fvisibility=default"],
+        }),
         exported_headers = subdir_glob(
             [
                 ("", "torch/csrc/jit/mobile/*.h"),
@@ -1185,7 +1195,10 @@ def define_buck_targets(
         srcs = [
             "torch/csrc/jit/mobile/observer.cpp",
         ] + ([] if IS_OSS else ["torch/fb/observers/MobileObserverUtil.cpp"]),
-        compiler_flags = ["-fexceptions"],
+        compiler_flags = ["-fexceptions"] + select({
+            "DEFAULT": [],
+            "ovr_config//os:macos": ["-fvisibility=default"],
+        }),
         header_namespace = "",
         exported_headers = subdir_glob(
             [
@@ -2035,7 +2048,7 @@ def define_buck_targets(
             "ovr_config//os:xtensa-xos": [
                 "-fdata-sections",
                 "-ffunction-sections",
-            ],
+            ]
         }),
         exported_preprocessor_flags = get_pt_preprocessor_flags() + [
             "-DMIN_EDGE_RUNTIME",

third_party/xnnpack.buck.bzl

@@ -2249,6 +2249,10 @@ def define_xnnpack(third_party, labels = [], XNNPACK_WINDOWS_AVX512F_ENABLED = F
         exported_deps = [
             ":subgraph",
         ],
+        compiler_flags = select({
+            "DEFAULT": [],
+            "ovr_config//os:macos": ["-fvisibility=default"],
+        }),
         platforms = (APPLE, ANDROID, CXX, WINDOWS),
         preprocessor_flags = XNN_COMMON_PREPROCESSOR_FLAGS + [
             "-DXNN_NO_Q8_OPERATORS",