libphobos: Increase size of defaultStackPages on OSX X86_64 targets.

As of macOS 11, libunwind now requires more stack space than 16k, so
default to a larger stack size. This is only applied to X86 as the
PAGESIZE is still 4k, however on AArch64 it is 16k.

libphobos/ChangeLog:

	* libdruntime/core/thread/fiber.d (defaultStackPages): Increase size
	on OSX X86_64 targets.

1 files changed, 10 insertions, 0 deletions

diff --git a/libphobos/libdruntime/core/thread/fiber.d b/libphobos/libdruntime/core/thread/fiber.d
index f4c04ce7358..2f90f179edb 100644
--- a/libphobos/libdruntime/core/thread/fiber.d
+++ b/libphobos/libdruntime/core/thread/fiber.d
@@ -595,6 +595,16 @@ class Fiber
         // the existence of debug symbols and other conditions. Avoid causing
         // stack overflows by defaulting to a larger stack size
         enum defaultStackPages = 8;
+    else version (OSX)
+    {
+        version (X86_64)
+            // libunwind on macOS 11 now requires more stack space than 16k, so
+            // default to a larger stack size. This is only applied to X86 as
+            // the PAGESIZE is still 4k, however on AArch64 it is 16k.
+            enum defaultStackPages = 8;
+        else
+            enum defaultStackPages = 4;
+    }
     else
         enum defaultStackPages = 4;