Implement sigsetjmp and siglongjmp for darwin/aarch64 (#139555)

libc/config/darwin/aarch64/config.json

@@ -0,0 +1,8 @@
+{
+  "setjmp": {
+    "LIBC_CONF_SETJMP_AARCH64_RESTORE_PLATFORM_REGISTER": {
+      "value": false,
+      "doc": "Avoid setjmp saving the value of x18, and longjmp restoring it. The Apple AArch64 ABI specifies that this register is reserved and should not be used"
+    }
+  }
+}

libc/config/darwin/aarch64/entrypoints.txt

@@ -101,6 +101,17 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.stdlib.free
 )
 
+if(LLVM_LIBC_FULL_BUILD)
+  list(APPEND TARGET_LIBC_ENTRYPOINTS
+    # setjmp.h entrypoints
+    libc.src.setjmp.longjmp
+    libc.src.setjmp.setjmp
+    libc.src.setjmp.siglongjmp
+    libc.src.setjmp.sigsetjmp
+  )
+endif()
+
+
 set(TARGET_LIBM_ENTRYPOINTS
     # complex.h entrypoints
     libc.src.complex.creal

libc/config/darwin/aarch64/headers.txt

@@ -7,6 +7,7 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.inttypes
     libc.include.limits
     libc.include.math
+    libc.include.setjmp
     libc.include.stdlib
     libc.include.string
     libc.include.strings