Increase minimum macOS SDK from 10.13 to 10.14 (#648)

Increases the minimum macOS SDK and the macOS deployment target from
10.13 to 10.14.

Also enables aligned allocations on macOS. We previously set
`-fno-aligned-allocation` on macOS since it was unsupported for arm64
prior to macOS 10.14.

Issue: flutter/flutter#114445

build/config/compiler/BUILD.gn

@@ -176,11 +176,6 @@ config("compiler") {
         "-arch",
         "arm64",
       ]
-      if (is_mac) {
-        # Aligned allocations are only supported on arm64 after macOS 10.14,
-        # however our deployment target is currently 10.11.
-        common_mac_flags += [ "-fno-aligned-allocation" ]
-      }
     }
 
     cflags += common_mac_flags

build/config/mac/mac_sdk.gni

@@ -6,11 +6,11 @@ import("//build/toolchain/goma.gni")
 
 declare_args() {
   # Minimum supported version of the Mac SDK.
-  mac_sdk_min = "10.13"
+  mac_sdk_min = "10.14"
 
   # The MACOSX_DEPLOYMENT_TARGET variable used when compiling.
   # Must be of the form x.x.x for Info.plist files.
-  mac_deployment_target = "10.13.0"
+  mac_deployment_target = "10.14.0"
 
   # Path to a specific version of the Mac SDK, not including a backslash at
   # the end. If empty, the path to the lowest version greater than or equal to