Suppress function UBSan on macOS

"-fsanitize=function" is designed to catch when calling a function
through a pointer of the wrong type (much like "-fsanitize=cfi-*call",
but a completely different mechanism). However, this is currently known
to have issues on macOS [0].

[0] llvm/llvm-project#109074

Change-Id: I66f51d8190f6105f852676a8faaf694e7f0dbcca
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/903958
Reviewed-by: Kaylee Lubick <kjlubick@google.com>

gn/skia/BUILD.gn

@@ -366,6 +366,10 @@ config("default") {
       "-fno-sanitize-recover=$sanitizers",
       "-fsanitize-blacklist=$_suppressions",
     ]
+    if (is_mac) {
+      # https://github.com/llvm/llvm-project/issues/109074
+      cflags += [ "-fno-sanitize=function" ]
+    }
 
     if (is_win) {
       cflags += [