[Bug target/80204] macosx-version-min wrong for macOS Sierra 10.12.3

[simon at pushface dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80204

--- Comment #3 from simon at pushface dot org ---
Created attachment 42077
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42077&action=edit
Patch to gcc/config/darwin-driver.c