Bump minimum macOS version from 10.9 to 10.13 for x86_64-apple-darwin

Author: zanieb

cpython-unix/targets.yml

@@ -546,7 +546,7 @@ thumb7k-apple-watchos:
 
 # Intel macOS.
 #
-# We target compatibility with macOS 10.9+ for compatibility with older Apple
+# We target compatibility with macOS 10.13+ for compatibility with older Apple
 # machines.
 x86_64-apple-darwin:
   host_platforms:
@@ -566,7 +566,7 @@ x86_64-apple-darwin:
   target_cflags:
     - '-arch'
     - 'x86_64'
-    - '-mmacosx-version-min=10.9'
+    - '-mmacosx-version-min=10.13'
     # Suppress extremely verbose warnings we see with LLVM 10.
     - '-Wno-nullability-completeness'
     - '-Wno-expansion-to-defined'
@@ -581,7 +581,7 @@ x86_64-apple-darwin:
   target_ldflags:
     - '-arch'
     - 'x86_64'
-    - '-mmacosx-version-min=10.9'
+    - '-mmacosx-version-min=10.13'
   needs:
     - autoconf
     - bzip2