[llvm] [bazel] Improve libc build on macOS (PR #86174)

[Keith Smiley via llvm-commits]

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@@ -992,10 +999,15 @@ libc_support_library(
 libc_support_library(
     name = "__support_osutil_quick_exit",
     hdrs = ["src/__support/OSUtil/quick_exit.h"],
-    textual_hdrs = [
-        "src/__support/OSUtil/linux/quick_exit.h",
-        #TODO: add support for GPU quick_exit (isn't just in a header.)
-    ],
+    textual_hdrs = select({
+        "@platforms//os:macos": [
+            "src/__support/OSUtil/darwin/quick_exit.h",
+        ],
+        "//conditions:default": [
+            "src/__support/OSUtil/linux/quick_exit.h",
+            #TODO: add support for GPU quick_exit (isn't just in a header.)
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keith wrote:

i can wait for yours, there's no rush on this one

https://github.com/llvm/llvm-project/pull/86174