Fix #9386: compilers failing to compile with LTO by using variants instead of new + unique_ptr

With std::variant all memory can be figured out at compile time, so the compiler needs to keep track of fewer elements. It also saves out a unique_ptr and its memory management, over a slight impact for resolving a setting.

.github/workflows/ci-build.yml

@@ -157,7 +157,7 @@ jobs:
 
     runs-on: macos-latest
     env:
-      MACOSX_DEPLOYMENT_TARGET: 10.9
+      MACOSX_DEPLOYMENT_TARGET: 10.14
 
     steps:
     - name: Checkout

.github/workflows/release.yml

@@ -470,7 +470,7 @@ jobs:
 
     runs-on: macos-10.15
     env:
-      MACOSX_DEPLOYMENT_TARGET: 10.9
+      MACOSX_DEPLOYMENT_TARGET: 10.14
 
     steps:
     - name: Download source